NRP Scientists

NRP conducts research on complex problems in the hydrologic sciences and supports research and development needs of the other USGS water-resources programs, other USGS Mission Areas and the priorities of U.S. Department of the Interior. The efforts of the NRP are multidisciplinary and require collaborative efforts among scientists within the NRP, other USGS programs, in Federal and State agencies, universities, and foreign countries. Research within NRP spans several subdisciplines. Each subdiscipline is represented by research scientists who serve as a Research Advisor to NRP managers and are a peer resource for scientists.

Below is a list of our Research Scientists with descriptions of their research. Lead scientists are indicated by (LS), and Research Advisors are indicated by RA.

The overall objective of this project is to determine the role of chemical processes associated with dissolved organic carbon (DOC) on the transport and reactivity of both naturally occurring and anthropogenic compounds. Defining the roles of DOC in environmental and geochemical processes is critical to understanding the nature and quality of the Nation’s water resources, and is important for future management of these resources. This field of study has increased in relevancy as numerous environmental problems have been linked to processes involving organic matter. My project attempts to meet these needs by focusing on the chemical mechanisms controlling the fate, transport, and reactivity of naturally occurring organic matter in aquatic systems. Main research topics include:

- Influences of DOM on the biogeochemistry of Hg and other metals, - Effects of hydrology and climate change on DOM in northern systems, including the Yukon River, - Influences of terrestrially derived DOM on satellite based assessments of water quality in the Gulf of Maine, and, - Development of improved methods for studying DOM composition and reactivity.

I conduct research focused on understanding the role of microorganisms on both contaminated and pristine ecosystems. I carry out this work using a polyphasic approach that combines microbiology, molecular biology, and biogeochemistry to understand microbial processes. My work specifically aims to (1) assess the impact of microorganisms on the fate of organic and inorganic contaminants; (2) to investigate the microbial role in metal cycling, e.g., iron, uranium, and manganese cycling; (3) evaluate the potential of microbial populations to contribute to energy resources, either through coal bed methane production or mitigating contaminants due to nuclear energy production or unconventional oil and gas production; and (4) to illuminate the unseen biodiversity in natural systems, such as caves and aquifers, and how this biodiversity impact biogeochemical cycles.

Determine source and sink strengths and environmental controls of greenhouse gases at the Earth’s surface and the role of management in modulating the exchange near the surface.
Evaluate the role of land use and climate change on evapotranspiration rates over various land surfaces toward regional assessments with the aid of models and remote sensing.

The overall objective of this project is to determine the role of chemical processes associated with dissolved organic carbon (DOC) on the transport and reactivity of both naturally occurring and anthropogenic compounds. Defining the roles of DOC in environmental and geochemical processes is critical to understanding the nature and quality of the Nation’s water resources, and is important for future management of these resources. This field of study has increased in relevancy as numerous environmental problems have been linked to processes involving organic matter. My project attempts to meet these needs by focusing on the chemical mechanisms controlling the fate, transport, and reactivity of naturally occurring organic matter in aquatic systems. Main research topics include:
1.) Influences of DOM on the biogeochemistry of Hg and other metals,
2) Effects of hydrology and climate change on DOM in northern systems, including the Yukon River,
3.) Influences of terrestrially derived DOM on satellite based assessments of water quality in the Gulf of Maine, and,
4.) Development of improved methods for studying DOM composition and reactivity.

My research can be broadly characterized as the use of statistics to simplify, understand and address complex, cross-disciplinary water resource problems. I have a particular interest in using statistics to arrive at parsimonious characterizations of natural systems and I am employing this philosophy to advance understanding in the areas of ecohydrology, sustainable water management at unmonitored locations, and trends in long-term environmental time series. By pioneering original insights into the statistical properties of streamflow time series, I am opening new pathways to determine surface-water availability at unmonitored locations and to classify streamgauges into ecologically-relevant management groups. My collaborations with colleagues from several countries led to a joint study to evaluate the use of multi-model frameworks to leverage the advantages, and overcome the limitations, of individual streamflow estimation models. With the recognition that hydrology is a changing system, I am working to quantify and attribute long-term changes in hydrologic time series.

My research program is multifaceted and involves the development of integrated hydrological, geochemical, and biological knowledge on the source-to-receptor approach to assessing impacts of emerging contaminants (hormones, personal care products, pharmaceuticals, commercial cleaning products). This applied research is targeted on issues important to water-resource managers and policy makers, and the results communicated to a spectrum of stakeholders.
The current focus of my research is the impact of biologically-active contaminants on aquatic organisms, and the relationship to receiving water (surface water and groundwater) attenuation capacity. Several major classes of contaminants are being investigated – endocrine disrupting chemicals, antibiotics, antidepressants, pharmaceuticals. Using a landscape-based approach, watershed-scale (from second-order streams to continental rivers) evaluation of chemical loading and fate, combined with field and laboratory exposure experiments, are used to develop a holistic understanding of contaminant behavior and impacts on ecosystem and human health. A key to this research is establishing interdisciplinary research teams to provide comprehensive evaluation of hydrology, chemistry, and biology. An applied aspect of my research is to better understand the role of engineered systems, including traditional wastewater treatment plants as well as treatment wetlands, to provide solutions for water-quality improvement and ecosystem enhancement.

The goal of my biodegradation research is to understand the processes controlling the rate of biodegradation of contaminants in the subsurface. This understanding will form the basis of methods to increase degradation rates without causing further degradation of groundwater quality. Recent work has focused on the fate of crude oil and agricultural nitrate contamination in the subsurface.

Specific objectives for the crude oil research include: (a) determine the rate that contaminants are transported from the source zone; (b) provide an estimate of how long the spilled oil will continue to pollute the groundwater; and (c) determine the fate of products of biodegradation or so-called “secondary water quality impacts” of bioremediation.

Specific objects of the nitrate research include (a) determining what controls the transformation rate of nitrate in the subsurface; (b) determining the residence time of nitrate contamination in groundwater.

The present goal of the pore pressure and faulting modeling is to understand how fluid pressure migrates from waste water injection wells to seismogenic faults.

Biotic responses to climatic change or human manipulation are inherently complex because of wide differences in organism sensitivities and response times, the influence of history and scale, and the various interactions between organisms and with the physical system. In arid and semi-arid lands, which cover about 12.5 percent of the Earth's land surface, the effects of climatic variability on vegetation are greatly magnified, particularly because most plants exist near their physiological limits. How arid land vegetation might in turn affect climate is uncertain, though there is some indication that decreasing cover and increasing albedo could promote regional drought. Whether in response to projected Greenhouse climates or intensified land use, vegetation in such critical watersheds as the Rio Grande and Colorado River basins is apt to change in the near future. There is a need to understand the direction and rate of this change and how it might affect water use and availability in the region. The objectives of this project are to achieve a dynamic understanding of vegetation change and its relation to water resources, to develop such an understanding in a manner appropriate to the hierarchy of spatial and temporal scales implicit in a study of global change, and to determine whether the responses of dryland vegetation to global change are predictable from past and present behavior of vegetation. For additional information, see the home page for the Desert Laboratory, which is operated jointly by the University of Arizona's Department of Geosciences, Department of Ecology and Evolutionary Biology, and the U.S. Geological Survey.

Improve understanding of physical and biogeochemical processes affecting water quality of groundwater and surface water. Research focus includes multidisciplinary field and laboratory studies to determine factors affecting sources, movement, and fate of nutrients and reactive inorganic contaminants in the hydrologic cycle.

Improve the usefulness of stable isotopes and other environmental tracers in hydrology and biogeochemistry by developing new techniques and approaches. Research topics include analytical techniques for stable isotopes in compounds separated from groundwater and surface water, stable isotope forensics, enriched isotope tracer experiments to quantify transport and reaction rates, field and laboratory determinations of isotope fractionation factors, numerical modeling of isotope effects during transport and reaction, interpretation of atmospheric tracers in groundwater dating and contaminant transport.

The overarching objective is to understand how anthropogenic sources of inorganic contaminants (metals) affect the structure and function of aquatic ecosystems. Elements of the research include: 1) develop and apply analytical methods and models to understand and predict metal bioavailability and bioaccumulation in aquatic organisms; 2) define effects of metal exposure on aquatic species; 3) communicate research findings to scientific and regulatory communities to support the management of water resources.

The project focuses on the use of analytical techniques that we have developed to support a wide range of studies in water-rock interaction, integrating solid phase mineralogy and elemental chemistry and clay mineralogy into hydrologic and contaminant studies.

The objective of this research is to study and quantitatively describe the factors that influence the response of macroinvertebrates to both anthropogenic and natural environmental factors and assess the effects macroinvertebrates have on the physical, chemical, and biological quality of aquatic systems. This involves 1) studying macroinvertebrate distributions across a range of spatial and temporal scales representing a variety of environmental settings and influences, 2) identifying and measuring the effects of stressors that are macroinvertebrate-specific, 3) identifying the effects macroinvertebrates have on the physical, chemical, and biological environment, 4) developing and applying statistical models that logically and rigorously address environmental and biological variability, and 5) identifying the influences of methodological factors on estimated macroinvertebrate responses and influences. This project has completed a number of “tasks” and will complete additional “tasks” in the future.

To better understand climate variability and possible climate change effects on surface hydrology, water resources and related natural and human managed systems in the western U.S., with emphasis on California.

Phytoplankton photosynthesis drives many biogeochemical and ecological processes in lakes, estuaries, and the ocean. For example, dynamic changes in pH, trace metal speciation, and concentrations of dissolved gases (oxygen, carbon dioxide, methane), inorganic nutrients (nitrate, phosphate, silicate), and organic compounds (amino acids, organosulfur compounds) are all closely associated with fluctuations in phytoplankton photosynthesis. Trophic linkages also exist, between the phytoplankton as primary producers and populations of consumer organisms including bacteria, zooplankton, benthic invertebrates, and fish. Our scientific understanding of lakes and estuaries as dynamic ecosystems is therefore dependent upon a mechanistic understanding of both natural and human-induced variability of phytoplankton abundance, community composition, productivity, and connections to geochemical processes and other biological communities. These topics are central to poorly resolved issues such as: the growing worldwide incidence of toxic algal blooms and associated fish mortality, coastal eutrophication and increasing frequency/extent of hypoxia or anoxia, long-term and cyclic changes in fish stocks, the global significance of phytoplankton to the cycling of key elements such as carbon and nitrogen, and ecosystem- scale responses to both species extinctions and introductions of exotic species. This project's objectives are to: (1) study the distribution, abundance, species composition, and productivity of planktonic microalgae, animals, and bacteria in estuaries, (2) define and quantify processes that regulate population dynamics and productivity of planktonic organisms in estuaries, (3) define and quantify processes through which the plankton alter and reflect water quality in estuaries, (4) define and quantify benthic processes that affect plankton dynamics and productivity of estuaries, and, (5) define anthropogenic impacts on estuarine ecosystems. For additional information, see San Francisco Bay water quality page.

Objectives are quantitative scientific examination of hydrologic processes in the near-stream environment to determine spatial and temporal patterns of stream exchanges with shallow ground, for the purpose of improved understanding of streambed exchanges and resulting impacts on water resources and stream ecology.

This project studies evaporation, groundwater mixing, surface-water circulation, groundwater/surface-water interactions, contaminant migration and remediation, and other hydrochemical and biologic processes. The isotope variations are related to (1) purely physical processes, (2) heterogeneous chemical equilibria, and (3) reaction kinetics. The isotope effects of many of these processes are not sufficiently understood or quantified to make the most effective use of stable isotope techniques in hydrologic research. This project aims to develop theoretical and instrumental mass spectrometric techniques through experimental investigation, and to test applications in suitable field locations to improve the utility of light stable isotope phenomena in hydrogeologic and biochemical studies.

Specific approaches of the project include (1) development of new or modified techniques for isotope analysis, (2) preparation and calibration of reference materials for international calibration of isotope-ratio measurements, (3) development of information management systems and quality control guidelines for stable isotope laboratories, and (4) testing applications of isotope measurements and theory, along with other types of hydrochemical data, in representative field settings. Experimental results and field data are used to improve understanding and develop predictive theoretical models of the processes involved.

I conduct long-term investigations on the fate and geochemical effect of organic contaminants in subsurface environments. I use a combined field and laboratory approach in a variety of hydrogeologic environments in order to meet these objectives. The principal questions being addressed by this project are: 1. How do long-term changes in biogeochemical processes affect the fate of organic and inorganic constituents in aquatic environments? and 2. Does availability of electron acceptors and electron donors control the progress of degradation reactions? My overarching objective is to increase our understanding of the transformation of contaminants from hydrocarbon spills, wastewaters from oil and gas development, and landfill leachate, and how those transformation processes impact aquifer and wetland chemistry over the long-term. My research has been largely at Toxic Substances Hydrology sites and is highly interdisciplinary, focusing on the coupled hydrogeological, microbiological, and geochemical processes that control the redox potential of subsurface systems and are a fundamental issue in understanding nutrient and contaminant biogeochemical cycles and in protecting drinking water and ecosystem health.

iv) To develop approaches that use isotopically modified metals, metal nanoparticles and metal bound to distinct mineral phases (such as Cu on ferric oxides) to quantify their bioavailability and toxicity to organisms, in particular invertebrates;

v) To use enriched metal isotopes to gain mechanistic understanding of the key processes controlling metal bioavailability, for example, to quantify the relative importance of ion uptake and (nano)particle uptake

To better understand and predict variability and recent changes in the responses of rivers, groundwater, and water/living resources, mostly in the West, to natural and human-induced climatic influences.

I conduct research on the transport and fate of organic contaminants in aquatic systems (terrestrial and marine). This entails field investigations and laboratory experiments that are designed to advance our understanding of natural processes and the effects of these processes on the behavior, mobility, and geochemical fate of organic chemicals of concern. I develop and apply new sampling and analytical techniques, identify potential molecular tracers, and develop models to predict contaminant fate. The laboratory I supervise houses analytical instrumentation that is used for detailed characterization of complex mixtures of organic chemicals as well as quantitative determination of targeted substances at ultra-trace levels. Although of modest size, my project is typically engaged in a number of studies at any given time.

Contaminants; Groundwater Flow and Transport; Groundwater-Surface Water Interactions; Water Quality

Watershed-scale water quality and water availability are affected by the interaction between the landscape and surface and subsurface flows at multiple scales. Wide-spread agriculture leads to diffuse non-point sources of contamination by agricultural chemicals. Localized exchanges of surface water and groundwater through highly reactive streambeds can attenuate the impact of agricultural chemicals on water quality. Thus, understanding the patterns and trends in water quality within a watershed requires analyses at multiple scales to understand hydrologic processes and the integration of hydrology and water quality information. The main objective of my research is to develop a better understanding of the role of groundwater flow and transport on watershed system behavior. Understanding surface water – groundwater interaction is an important part of this is. Analyses of field data and simulation are used to characterize water and chemical mass balances in order to understand the relative importance of different flow pathways. Another objective of my research is to compare and contrast surface water-groundwater interactions and chemical fate in different hydrologic/environmental settings. Models developed for these studies can be used to test the impact of different management/remediation scenarios on water quantity/quality.

Human activities from climate change to waste discharges to water management are modifying ecosystems across the earth, often in ways that are not well understood. This project addresses the problem of better understanding changes in aquatic ecosystems as driven by human disturbances interacting with natural processes. More specifically, the project studies a) the mechanisms of biological and ecological response to stressors such as metal contamination, nutrient enrichment, physical habitat alteration, climate change, and introduced species, and b) the influence of species, communities, and ecosystem processes on the distribution, transport, and fate of chemical contaminants (e.g., metals, nutrients). Most studies on the project ultimately consider physical, chemical and biological processes that interact in ecosystem change, as well as mechanisms of stressor-specific responses in species, populations, and communities, with an emphasis on invertebrate organisms/communities. Both intensive laboratory and field experimentation as well as long term field observation are typical of project work. An important goal is development of models to improve understanding of biological and ecological responses to stressors. For example, biodynamic models are an important focus of metal contamination studies (and studies of the implications of developing nanotechnologies) because they provide a mechanistic explanation of many biological and ecological responses to metals. These models are based upon laboratory-based experimental studies of contaminant uptake, loss and detoxification in different species linked to field observations of contaminant concentrations. Understanding differences in contaminant biodynamics, when linked with carefully designed studies of benthic communities, for example, can lead to process-based predictions of ecological change. Ongoing or past project includes studies in streams, rivers, lakes and estuaries. Historically, the project has introduced many new methodologies. Continued refinement of those and the development of novel new methods is another important ongoing and future goal of this project. Perpetuation of long-term (multi-decadal) ecological, metal and geochemical data sets, in collaboration with non-USGS partners, is also an ongoing goal in ecosystems from South San Francisco Bay, North San Francisco Bay, Santa Clara Valley streams, and the Clark Fork River Montana. The unique capacity to integrate laboratory and field studies across levels of biological organization in diverse aquatic ecosystems establishes our ability to identify, tackle, and inform managers and scientists of newly emerging issues which is a critical need of the USGS and an important part of our work into the future. For additional information, see
Ecology and Contaminants site.

The focus of my research is to characterize the processes and mechanisms of metal sorption reactions with surfaces of natural solid phases (aquifer and stream sediments) through field studies and lab experiments with solid materials from the field and with model sorbent phases. Molecular scale characterization of sorbed metal speciation is needed for confirmation of reaction mechanisms to improve reaction terms in transport models, to assess long-term fate of attenuated metals in response to changing hydrologic and geochemical conditions, and to better understand the bioavailability of metal contaminants. In conjunction with lab and field experiments, my investigations utilize X-ray absorption spectroscopic (EXAFS) and microscopic techniques (e.g. X-ray microprobe; SEM-EDS) to quantify speciation of sorbed metals and to characterize sorbent phases. The goals of this research are to improve our ability to assess the potential for natural attenuation in contaminated systems, to improve reaction terms in transport models, to elucidate geochemical controls of metal bioavailability to aquatic organisms, and to facilitate improved design and assessment of remediation strategies. My research focuses primarily on sites contaminated by hard rock mining activities.
My research also includes the use of environmental radioisotopes (
210Pb,
137Cs,
7Be,
234Th) to determine sediment chronology in lakes, reservoirs and estuaries for reconstructing contaminant input histories, sources of suspended sediments, and soil and wetland chronology for rates of carbon turnover, in collaboration with WSC, NAWQA, GD projects and university scientists.

Evaluate the hydrologic and geochemical processes that control nitrate fluxes in agricultural settings. Important questions remain about the overall regional and global importance of groundwater nitrogen fluxes, denitrification (microbial reduction of NO
3− to N
2), and the sources of electron donors contributing to this microbial reaction. Studies are needed that apply robust methods for measuring nitrogen fluxes and denitrification among multiple sites to evaluate important factors affecting N fluxes. These results, in combination with novel methods for efficient estimation of fluxes in groundwater, facilitate estimates of N fluxes in across large regions such as the Corn Belt.
Quantify the effects of complex geology on flow and reactive transport of groundwater contaminants and on interpretation of tracer data from monitoring wells. The USGS and NAWQA have made a large investment in sampling monitoring wells and production wells to understand water quality status and trends as well as geochemistry of major aquifers. In most aquifers, geological complexity complicates the interpretation of the data from these samples. I develop and apply innovative methods to evaluate effects of geological variability on concentrations of environmental tracers and contaminants. Application of these methods allows a better understanding of the true, in-situ reactions and long-term trends in concentrations.

Predicting the outcome of flow and sediment transport events quantitatively has been difficult due to the complex nature of stream systems and the effects of woody vegetation on flow and sediment transport. Interactions between channel and floodplain flow, sediment transport, and woody vegetation have important implications for the health of riparian vegetation and as well as for contaminant transport and deposition. The goal of my research is to develop methods for the application and testing of predictive, process-based models (no empirically adjusted coefficients) that compute the flow and sediment transport from fluid mechanical theory for (1) known channel and floodplain topography and (2) measured tree and shrub characteristics. My recent research has focused on the Rio Puerco arroyo in north-central New Mexico, where large-scale geomorphic changes related to differing distributions of woody vegetation continue. I integrate geomorphic data obtained from various sources and at various scales, including imagery, high-precision GPS survey data, and high-resolution LiDAR topography, and I use these data to perform spatial analyses of geomorphic change through time within the Rio Puerco arroyo. Physical characteristics and distributions of woody vegetation and topography determined from field measurements and remote sensing data are converted to local hydraulic roughness fields, from which the friction on the sediment surface, needed to compute the sediment transport, can be determined. Computations of flow and suspended sediment transport are tested using data obtained after a large flood in August 2006.
Another focus of my research is on assessing potential effects of future climate change on the health of the riparian cottonwood forest in Theodore Roosevelt National Park, ND. The first goal in this project is to determine the variability in historical weather patterns throughout the Little Missouri River basin and relations between observed weather, streamflow, and tree-ring growth. Once we have developed an understanding of these processes, we will apply a precipitation-runoff model using down-scaled climate predications to estimate the effects of future climate change on the health and extent of the riparian forest.

The goal of my research is to develop innovative approaches for the detection trace gases and expanding our understanding of their environmental cycles. Dissolved gases can be used as age tracers and climate markers, provide information about biological activity and recharge conditions, and provide unique fingerprints of superficial activity in aquifer systems. This sort of information is valuable to both scientific and resource management communities, and there are many benefits to enhancing our knowledge of the class of compounds.

The “Hydroecology of Flowing Waters” project was initiated in 1998 with the aim to improve understanding of how stream and river corridors function naturally in ways that produce valuable ecosystem services (e.g. flood attenuation, carbon and nutrient storage and contaminant removal, habitat value for fish and wildlife, recreation). The research is increasingly focused on how aquatic ecosystem services can be better protected in the face of degradation resulting from accelerating land use and climate change. Central to the research is the investigation of interactions between physical and biological processes, e.g. how land use change affects hydraulics and channel geomorphology in ways that produce cascading effects on hydraulic residence time, hyporheic exchange flux with sediments, stream metabolism and related biogeochemical reactions such as denitrification and mercury methylation, and overall health of aquatic ecosystems. A focus is improving understanding of the effectiveness of river restoration in protecting ecosystem services. The goal is to better anticipate how natural and man-induced changes in water flow affect downstream water quality, quality of biological habitats, and overall sustainability of stream and river corridors in a changing world.

Our objectives are: • A better understanding of bacteria-contaminant interactions in ground water, because of the persistence of many contaminants in the subsurface environment and because of increasing demands for both high-quality ground water and on-land disposal of toxic chemicals. • A better understanding of microbial transport through the terrestrial subsurface because of the implications for public health (microbial contamination of wells) and because of its roles in groundwater ecology and in the fate of groundwater contaminants.

The overall objective of the MoWS research group is to gain better understanding of the precipitation-runoff processes and use this knowledge to develop improved hydrologic models. The main research topics include: 1) Add functionality and improvements to the MoWS simulation models being developed and integrate with other hydrologic, hydraulic, and climate models. 2) Enhance the models to use the best and latest topographic, climate, geologic, and land-use data sets as direct input to process algorithms to increase the physical nature and temporal and spatial resolution of model input. 3) Develop national model structure and calibration strategy for national model application.

Various processes within the unsaturated zone affect ground-water availability and portability, as well as concentrations of water vapor and trace gases in the atmosphere. The rate at which precipitation or applied irrigation water infiltrates, its redistribution following infiltration, and the partitioning of the redistributed soil moisture between ground-water recharge and evapotranspiration affect the rate at which the ground-water reservoir is replenished and the degree to which ground water might be contaminated by chemical applications, spills, or disposal. Consequently, knowledge of and methods to quantitatively measure and predict these processes are needed to determine the impact of such societal practices as irrigation development for agriculture, the use of agricultural chemicals, and the disposal of radioactive and/or hazardous waste in the unsaturated zone on both the availability and potability of ground water. Processes governing transport in the unsaturated zone gas phase are also important in determining the potential for ground- water contamination by volatile compounds, the rate at which water is returned from soil moisture to the atmosphere as vapor, and the fate of other "greenhouse gases", such as carbon dioxide, methane, and chlorofluorocarbons (CFCs). An understanding and quantification of these processes is needed both to assess the hazards of ground-water pollution and to better predict the impact of global change on future climate.

Using long-term data records, this project is focused on two problems of importance to water resources managers. First, long-term streamflow records are being used to a) identify broad regional to national trends in floods and low-flows and relate them to possible causes (climate change, water management changes, land-cover changes, and ground-water level change) and b) determine whether there are patterns that relate to watershed size or climate characteristics. It is often stated in the popular press and in official publications on global climate change that we can expect increased variability, including larger and/or more frequent floods, and deeper and longer droughts, as a result of greenhouse warming. This research will use the long-term historical records of streamflow at USGS streamgages to explore the empirical evidence for such statements. The second area of research is related to long-term changes in nutrient concentration and transport in major rivers. Although water resources managers have been attempting to control nutrients in our Nation's waters through efforts such as point source pollution control, non-point source best-management-practices, and air quality controls to limit atmospheric deposition, the question on how effective these efforts are remains unclear. The scientific complexities of this problem include consideration of: time lags between control measures and expected results, the potential that different control measures will have a different type of impact at low versus high flows or during some seasons and not others, and the potential for hysteresis in relationships between concentration and flow. The answer to this seemingly simple question is difficult to determine because surface-water quality is so highly dependent on the natural interannual variability of flow conditions.

My primary research objective is to evaluate ecosystem health in freshwater systems using biologically meaningful measures of metal exposure. Resident aquatic organisms accumulate metal into their tissue by integrating the metal from their environment (dissolved and diet). Using physiological parameters derived from earlier experiments, I am developing a model to predict biomonitor tissue concentrations under various exposure conditions. The goal of this research is to link biological responses to changes in environmental condition (e.g., remediation and physical disturbances associated with floods). While this work was developed from the Clark Fork River study, the model is applicable to other impaired rivers and streams.

The Lake-Atmosphere Interactions project (LAIP) develops and applies regional and global climate models and surface process models in the context of broadly interdisciplinary research aimed at addressing past, present and future climate hypotheses, questions and issues and at providing climate data for applied research. The project research is conducted across a wide range of temporal (the past 106 years and into the future) and spatial (global to local) scales. Project objectives are achieved by developing and applying a variety of numerical models, visualization techniques, web-based applications and statistical methods to quantify and explain interactions between the atmosphere, lakes, aquatic and terrestrial ecosystems, glaciers, and wildfire.

Develop, enhance, and extend theory and methods to investigate and characterize fluid flow, solute transport, heat transport, and stress/deformation changes in fractured and porous media for application to diverse areas, including the assessment of groundwater availability in bedrock terrains, remediation of contaminated sites, and evaluation of potential hazards such as induced seismicity from fluid injection.

Many hydrogeomorphic processes are poorly understood. Botanical evidence studies can improve flood or debris flow prediction for streams with short or no gaging-station records. Improvement of our understanding of the relations among fluvial geomorphology, sedimentation, mass wasting, plant chemistry, and plant ecology will provide insight into such problems as assessment of water quality, wetland loss, long-term effects of climatic variation, and the frequency and magnitude of destructive hydrogeomorphic phenomena. Botanical and geomorphic analyses may provide substantial information about variable source areas of runoff production and ground-water recharge. The general objectives of this project include: 1) the continued development of the combined use of botanical evidence and maximum likelihood estimators in flood-frequency prediction, 2) analysis and interpretation of the role of vegetation in natural and disturbed fluvial systems, including riparian and wetlands systems, 3) research in the hydrogeomorphic-plant ecological aspects of watershed dynamics, including the delineation of variable source areas of runoff production and ground-water recharge, and analyses of non-point source pollution and basic plant-landform relations and 4) use of tree-ring chemistry as an indication of ground and surface water quality.

Quantitative understanding of groundwater and gas-rich fluid- and thermodynamics in volcanic areas is important for several reasons: 1) as a major source of hazard such as propellant in steam-driven explosions, lubricant in mudflows, and transport agent for toxic constituents such as arsenic and mercury that are dissolved from fresh volcanic rock, 2) groundwater pressure, temperature and chemical changes might signal one of the earliest warnings of volcanic unrest, 3) exploration and mining of geothermal energy and mineral deposits. Many of the geochemical, geodetic, and seismic signals measured at the ground surface as part of the volcano monitoring strategies have hydrothermal origins or magmatic origins modulated by the intervening hydrothermal system.

My major research objectives are to characterize spatial and temporal patterns in volcano-hydrothermal systems and relate them to volcanic activity by interpretation of hydrologic, geochemical, geologic, and geophysical data. This research is intended to support the USGS Volcano Hazards Program’s broad goal of lessening the harmful impacts of volcanic activity and the USGS Geothermal Program to explore and develop technologies that will allow us to tap into reservoirs of geothermal heat that are known to exist in the Earth’s crust. Specific research questions include (1) What are the modes of heat and mass transport from magma to the shallow subsurface? (2) What are the pressure, temperature, and fluid-saturation conditions between magma and the land surface? (3) What controls the permeability of volcanoes? How does it vary in space and time? What role do temporal variations in permeability play in the evolution of volcanogenic hydrothermal systems? (4) How well-coupled are various fluid flow, transport, and mechanical deformation processes? (5) How can we evaluate hydrothermal systems in volcanoes dominated near the surface by cold ground-water recharge? (6) What is the interplay between groundwater transients, seismicity, and volcanic activity at various timescales?

Our research focuses on developing methods to analyze volcano-hydrothermal systems and on the application of these methods to particular volcanic systems in the western United States. Specific research questions include (1) What are the modes of heat and mass transport from magma to the shallow subsurface? (2) What are the pressure, temperature, and fluid-saturation conditions between magma and the land surface? (3) What controls the permeability of volcanoes? How does it vary in space and time? What role do temporal variations in permeability play in the evolution of volcanogenic hydrothermal systems and episodes of volcanic unrest? (4) How well-coupled are various fluid flow, transport, and mechanical deformation processes? (5) What is the interplay between groundwater transients, seismicity, and volcanic activity at various timescales?

Our project is unusual among NRP projects in that it has been funded by thrust programs traditionally housed in another former USGS Discipline – including all salary, common-services burden, and OE. Thus a bit of historical perspective may be useful. Since its inception in 1973, our project has been funded through interdisciplinary thrust programs, with an emphasis that has evolved from geothermal resource assessment (under the former Geothermal Research Program) to mitigation of volcanic hazards (under the current Volcano Hazards Program). Through the late 1980s the project had a heavy emphasis on research related to resource assessment, with a particular focus on the Basin and Range and Cascade Range provinces. As the program gradually re-oriented towards volcano-related public-safety issues, our project began to emphasize topical research relevant to volcanic processes such as geysering (Science, 1993; JGR, 1996; GRL, 2003; Geology, 2008; also many recent papers by my colleague Shaul Hurwitz), ground-water flow near cooling plutons (GRL, 1994; JGR, 1997; JGR, 2003; RoG, 2010), and volcano seismicity (EPSL, 2005). We also placed an increasing emphasis on fieldwork on active volcanoes such as Kilauea (e.g. WRR, 1996; JGR, 2002; JGR, 2003; GRL, 2003; GRC Bulletin, 2003), the Three Sisters (GRL, 2002; Geology, 2004; Geofluids, in review), and Yellowstone (JVGR, 2007; Elements, 2008; Geology, 2008; G3, 2012; JGR, 2012; GRL, 2013). At the same time, we extended numerical models originally developed for geothermal-reservoir simulation to describe phenomena such as water-table position in stratovolcanoes (JGR, 2003) and the coupling between hydrothermal-fluid dynamics and crustal deformation (JGR, 2007; JGR, 2009). Our overall research focus shifted from one-time “snapshots” of volcanic systems towards active monitoring that can potentially complement other ongoing geophysical data streams (e.g. seismicity and geodesy) (JVGR, 2001; JVGR, 2007; JVGR, 2010; Geofluids, in review). Over the last several years we have again received substantial funding from the revitalized USGS Geothermal Program, which is housed in the Energy, Minerals, and Environmental Health Mission Area. The funding from the Volcano Hazards and Geothermal Programs is complementary, because the programs share an interest in hydrothermal systems.

The purpose of my research group is to develop new methods and applications of environmental isotopes to solve problems of national importance. In specific, the overall goal is to use environmental isotopes, combined with other biogeochemical measurements and hydrologic and biogeochemical modeling, to increase our understanding of biogeochemical and hydrological processes, nutrient and organic matter sources, subsurface flowpaths, and water age distributions in diverse environments.

Many of our studies piggyback on the sampling efforts of major monitoring programs to investigate causes of hypoxia and food web problems. Our work provides critical scientific support for these monitoring programs. A long-term career goal is the development of a portfolio of isotope and other tools for piggybacking onto state and federal monitoring programs for ecosystem studies.

a) Developing defensible conceptual models of processes influencing the mass transfer of inorganic contaminants between aqueous and solid phases.
b) Translating conceptual models into quantitative models that can be used to predict the influence of mass-transfer processes on contaminant fate and transport in field applications.
c) Developing approaches to obtain parameters required to describe contaminant mass transfer in quantitative fate and transport models that are, to the maximum extent possible, independent of field observations.
d) Testing these approaches in laboratory experimental studies, field experimental studies, and field-scale plume characterization studies.

Phytoplankton photosynthesis drives many biogeochemical and ecological processes in lakes, estuaries, and the ocean. For example, dynamic changes in pH, trace metal speciation, and concentrations of dissolved gases (oxygen, carbon dioxide, methane), inorganic nutrients (nitrate, phosphate, silicate), and organic compounds (amino acids, organosulfur compounds) are all closely associated with fluctuations in phytoplankton photosynthesis. Trophic linkages also exist, between the phytoplankton as primary producers and populations of consumer organisms including bacteria, zooplankton, benthic invertebrates, and fish. Our scientific understanding of lakes and estuaries as dynamic ecosystems is therefore dependent upon a mechanistic understanding of both natural and human-induced variability of phytoplankton abundance, community composition, productivity, and connections to geochemical processes and other biological communities. These topics are central to poorly resolved issues such as: the growing worldwide incidence of toxic algal blooms and associated fish mortality, coastal eutrophication and increasing frequency/extent of hypoxia or anoxia, long-term and cyclic changes in fish stocks, the global significance of phytoplankton to the cycling of key elements such as carbon and nitrogen, and ecosystem- scale responses to both species extinctions and introductions of exotic species. This project's objectives are to: (1) study the distribution, abundance, species composition, and productivity of planktonic microalgae, animals, and bacteria in estuaries, (2) define and quantify processes that regulate population dynamics and productivity of planktonic organisms in estuaries, (3) define and quantify processes through which the plankton alter and reflect water quality in estuaries, (4) define and quantify benthic processes that affect plankton dynamics and productivity of estuaries, and, (5) define anthropogenic impacts on estuarine ecosystems. For additional information, see
San Francisco Bay water quality page.

In collaboration with scientists from other agencies and academic institutions, studies focus on quantifying the importance of benthic sources of biologically reactive inorganic solutes (for example, dissolved macronutrients and trace metals). The importance is quantified and compared to other solute transport processes (for example, advective transport) and biological requirements for primary production in a wide range of oligotrophic to hypereutrophic aquatic systems. Such results provide critical input to the development and refinement of water-quality (e.g., TMDL) models that must evaluate alternative management scenarios.

Reconnaissance and chemical and isotope sampling of thermal springs in the western United States has not generally provided information of sufficient detail to permit the geothermal potential of most individual areas to be determined with any certainty. This is especially true in the Cascade Mountain Range, where the chemical geothermometers indicate much lower temperatures of water-rock equilibrium than the sulfate-isotope geothermometer and the geologic setting seem to require. This discrepancy could be due to simple mixing of thermal and fresh water or rapid equilibration of water with the surrounding country rock as the fluids rise to the surface; alternatively, the sulfate-isotopic composition could be an artifact reflecting the original source. In this project, the origin of the dissolved constituents, water, and gases discharging in the hot springs will be investigated, their relationship to the fumaroles and cold mineral springs ascertained, and recharge areas for the thermal springs and the amount of mixing of thermal and nonthermal waters will be determined. For additional informaition, see the Dynamics of Volcano-Hydrothermal Systems web site.

My objectives are to answer scientific questions including:
How do coupled physical and biological processes influence phytoplankton, the base of the aquatic food web? This question is important because many symptoms of impairment in coastal and inland waters (e.g. hypoxia related fish kills, toxic algae related shellfish mortality, waterbird poisoning, and human illness) are related to phytoplankton species or concentrations. Phytoplankton also provides a critical, sometimes limiting source of organic carbon at the aquatic food web base that can regulate organism recruitment and survival at higher trophic levels (e.g. zooplankton and fish). Moreover, because phytoplankton is “food” for consumer organisms, it represents a means of contaminant entry to upper trophic levels.

How can we integrate scientific disciplines (physics and biology) and scientific approaches (numerical modeling and field measurements) to better understand how climate, hydrology, hydrodynamics, chemistry, sediment dynamics, exotic species, and resource management together influence aquatic ecosystems? To understand contemporary and historical physical-chemical-biological interactions, we rely on measurements and process based models. To assess how these interactions might work in the future, new modeling approaches---ground-truthed by observations---must be developed. Our understanding of the approaches best suited to studying these interactions and future scenarios is far from complete.

How will ecosystem functions and services shift in response to changes in climate, management, or physical configuration? Aquatic ecosystems around the globe are facing multiple interacting forces of change into the coming decades. Ecosystem services in many cases are already stretched and degrading, and it is currently unknown how most ecosystems will function in the future under the influence of drivers including climate change, water management, non-native species invasions, and ecosystem restoration. In the CASCaDE project, we are developing a series of linked models to assess possible futures for the Sacramento-San Joaquin Delta ecosystem in response to multiple interacting drivers. We expect our approach to transfer to other systems facing similar challenges.

How do aquatic habitats communicate with each other? Most aquatic habitats have at least upstream or downstream connections with other water bodies. Hydrodynamic processes provide inter-habitat communication by transporting biotic and abiotic particles and dissolved substances between habitats. Our research has demonstrated how such hydrodynamic connectivity can play a large role in determining the mass balance and ecological functionality of habitats and ecosystems. We are developing and applying observational, numerical, and theoretical approaches to better quantify and understand the processes and ramifications of inter-habitat connectivity.

The overall objective of the MoWS research group is to gain better understanding of the precipitation-runoff processes and use this knowledge to develop improved hydrologic models. The main research topics include:
1) Add functionality and improvements to the MoWS simulation models being developed and integrate with other hydrologic, hydraulic, and climate models.
2) Enhance the models to use the best and latest topographic, climate, geologic, and land-use data sets as direct input to process algorithms to increase the physical nature and temporal and spatial resolution of model input.
3) Develop national model structure and calibration strategy for national model application.

The objectives of my current research are to 1. Understand the water quality effects of fire, 2. Measure the effects of fire on the carbon cycle and other biogeochemical cycles, 3. Characterize the combustion products of wildfire, mainly ash and charcoal, and 4. Link post-fire responses and the composition, physical characteristics, and reactivity of ash and charcoal to measures of burn severity detected on the ground or using remotely-sensed data. The overarching objective of my research is to understand runoff, erosion, deposition, and water quality effects after wildfire.

The overarching objective of this Project is to determine how and why biogeochemical cycles of macronutrients (i.e. C, Fe, S, etc…) and those for certain trace contaminants (e.g. Hg, Se, As, etc…) covary at the ecosystem and regional scales. General approaches to this end include:

comparing and contrasting key biogeochemical pathways both within the sub-habitats of a given ecosystem and among systems that involve a wide range of land-use practices,

fostering collaborations with other USGS and non-USGS scientists on projects that are regional in scope, have a fundamental biogeochemical/microbiological focus, and that balance basic environmental research with management / society ‘needs-driven’ research

Climate displays an often-unrecognized order in both time and space. What may appear as a random sequence of precipitation at a point or within a watershed is actually the local expression of a broad integrated system of weather processes that are active on scales of 100’s to 1000’s of kilometers. Only when climate forcings and hydrologic responses are considered from a regional perspective does the order become evident. Understanding these regional processes provides a sound basis for national, regional, and local hydrologic analysis, resource management, and hazard assessment/mitigation. The objectives of this research are (1) to identify and quantify relations between large-scale atmospheric circulation and sea-surface temperatures and surface hydrologic variables (e.g. precipitation, snow, streamflow), (2) development of improved precipitation-runoff models, and (3) examination of the effects of climatic variability and change on water resources.

I conduct field and laboratory research on processes affecting the distribution of inorganic constituents in natural waters. Most of my research focuses on redox sensitive compounds of arsenic, chromium, iron, sulfur, and mercury. I also study conductivity methods and applications for natural waters. Field sites have included the Summitville mine, CO, the Boulder Creek watershed, CO, the Mojave Desert, CA, the Questa mine, NM, and Yellowstone National Park.

To advance understanding of the factors controlling the environmental fate of elements which may be toxic or of other concern (e.g. greenhouse gases). For instance, microbes influence the partitioning of group 15 and 16 elements (Phosphorus, Arsenic, and Antimony; Sulfur, Selenium, and Tellurium) between dissolved and adsorbed phases, strongly affecting the quality of drinking water in aquifers around the world. On another topic, it is well known that methane and nitrous oxide are strong absorbers of IR radiation and act as greenhouse gases near the Earth’s surface. Bacteria in lakes, wetlands, and soils both facilitate and mitigate the flux of these gases and in so doing, shape our world. The primary goal of the research is to determine how bacteria metabolize elements that in many cases are quite toxic. Another goal is to understand how microbes respond to various environmental stresses (e.g. salinity or temperature) in order to predict how the flux of an element or compound is likely to change in the context of a changing environment.

The objectives of my research are (1) to synthesize observational estimates of continental water and energy fluxes and storage; (2) to construct global computational models of continental water and energy fluxes and storage; (3) to identify physical controls, natural and anthropogenic, on spatial and temporal variability of water and energy fluxes and storage; and (4) to elucidate the hydrologic causes and effects of Earth-system variability and change, including climatic, biospheric, and geodetic processes.

This project focuses on sediment erosion and deposition processes associated with disturbed watersheds and the essential processes needed to predict evolution of river systems. The objectives are to understand: a. Spatial and temporal character of rainfall and the transformation of rainfall into runoff, which controls erosion and deposition. b. Hillslope runoff processes characterized by shallow, unsteady flow where the relative roughness causing friction can be much greater than, for example, in perennial channels with nearly steady flow. c. Geomorphic and scale effects of channel networks on the prediction of the runoff hydrographs. d. Coupling of biologic and geomorphologic processes to predict erosion and deposition on the time scale of individual floods, rather than longer time scales (years, decades, and centuries) of such processes as the erosion of stream banks by turbulent fluid flow, sediment deposition on floodplains, and the effects of woody riparian vegetation on channel flow, bank erosion, floodplain flow, and channel migration.

Project research is focused on two general objectives: first, to better understand the basic physics of coupled flow and sediment transport in geophysical flows; second, to develop practical tools based on that understanding that can be used in a predictive manner to aid in the management of the Nation’s rivers. Within the context of this overarching pair of long-term goals, the project has a number of specific shorter-term objectives, some of which are research oriented, and others of which are related to technology transfer or consultation on specific riverine issues. Our current research objectives are as follows: 1) Develop and test physically based methods for predicting the initiation, development, and response to time-varying flows of riverine bedforms (ripples and dunes). 2) Develop, test, and refine methods for predicting bar response to time-varying flows. 3) Develop, test and distribute algorithms that construct explicit linkages between physical river characteristics and habitat or other biological considerations. 4) Develop, test, and refine methods for collecting river bathymetry using remote-sensing techniques. This involves using multi/hyperspectral scans, visible-wavelength LiDAR, infrared videography and other optical techniques to determine river characteristics. 5) Develop new understanding and basic laboratory data sets on the interaction of turbulence and sediment transport. This work uses a combination of particle-image velocimetry, phase-Doppler velocimetry, and high-speed videography to develop relations between instantaneous flow conditions (including turbulent fluctuations) and sediment dynamics.

Our current objectives for technology transfer and consultation on specific riverine issues are as follows:

1) Develop, maintain, distribute, and provide training on state-of-the-art river modeling software. 2) Provide consultation, modeling services, review and oversight for the Kootenai River Restoration Project at the request of BPA and the Kootenai Tribe of Idaho. 3) Provide consultation, review, and oversight on river flow and sediment transport modeling for the Coeur D’Alene River Superfund site at the request of EPA. 4) Many smaller projects carried out cooperatively with USGS WSC staff and University researchers, including work on Copper River, Fountain Creek, Klamath River, Trinity River, Russian River, Green River, Colorado River, Platte River, Cedar River, Missouri River, Flint River, Red River, Mississippi River, etc.

Permeability – the ease of fluid flow through porous media – varies about 17 orders of magnitude in geologic media. My research concerns fluid and solute transport in the low part of the of the range (~ 10-19 – 10-25 m2), where measurements are difficult, standard relations such as Darcy’s law are unverified, and unfamiliar phenomena that include osmosis and ultrafiltration affect movement of water and solutes. Testing can sample only small volumes of low-permeability formations, and finding ways to characterize them on regional scales – and thereby detect leakage through fractures and faults - is especially important for problems such as repository siting, CO2 and other waste injection, and protection of aquifers. Understanding of how confining layers not only protect aquifers but also control their long-term productivity is needed to meet increasing water demands. Finally, low-permeability groundwater systems are of fundamental scientific interest because they record information about the processes of geological change.

The hydrogeology of low-permeability environments was historically bypassed and data are sparse, so fundamental aspects remain uncertain. For example, the roles of chemically-driven water flow and filtration of solutes continue to be debated. Measuring formation properties and groundwater pressure, and sampling groundwater itself still present serious technical challenges. My research focuses on (1) devising and improving testing and sampling techniques, (2) clarifying the nature and importance of various flow and solute transport processes, and (3) analyzing low-permeability flow systems to characterize how they control aquifer behavior, how they behave as barriers, and to understand their roles in groundwater flow systems and Earth processes.

To measure, predict, and understand the flow of water through the soil and rock of the unsaturated zone. Specifically to advance (1) knowledge of aquifer recharge rates for improved management of water resources, (2) the assessment and quantification of hazards from contaminants near the earth's surface, and (3) the understanding of soil moisture processes in relation to ecological habitat. Results are directed toward large-scale problems of water quality, water availability, land-use evaluation, and environmental impacts of climate change.

The objectives are to 1) Quantify the hydrogeomorphic and ecological controls of nutrient and contaminant fluxes in wetland ecosystems; 2) Scale wetland fluxes from site to watershed scale; and 3) Identify the principals and modeling tools for managing wetland and river ecosystems. The focus will be on floodplain ecosystems, which are poorly studied due to the challenges of working in this environment and their inherent complexity.

Aqueous chemical models have become popular tools for the interpretation of natural water chemistry. Unfortunately, these models have deficiencies because of (1) incorrect or inconsistent thermodynamic data, (2) invalid assumption regarding the equilibrium state, (3) inappropriate or invalidated corrections for nonideality, (4) inadequate expressions for temperature dependence, (5) invalidated limitations for ionic strength, composition and temperature, and (6) lack of data on solid solution solubility. The plethora of models and databases has prompted federal agencies, especially hazardous waste and nuclear waste managers, to request geochemical code validation. Acid mine waters are a major source of water pollution and provide one of the application of trace element speciation models. Objectives of this project are to develop, test, evaluate and make field applications of chemical models for equilibrium speciation and mass transfer of major and trace constituents in acid mine waters and ground waters.

Micro-organisms alter the chemistry and productivity of aquatic environments by performing complex transformations of organic and inorganic molecules. In many cases, microbes can affect the speciation, mobility, bioavailability, and toxicity of toxic elements, such as Se, Hg, and As. The mechanisms by which these reactions proceed, the in situ rates of the transformation, their quantitative significance to element cycling, the responsible microorganisms and their physiology are only poorly understood. In this project, conceptual models of biogeochemical transformations will be developed by the combination of lab and field experimental work. Laboratory work will focus on identification of biochemical pathways, isolation and physiological characterization of relevant microbes. Field work will consist of measuring in situ rates of transformations, based on methods developed in the laboratory. Physical exchanges between components, such as the flux of biogenic gases to or from the atmosphere from water or soil will be quantified.

My research goals are (1) to develop reaction-transport models with varying levels of complexity and data requirements, providing guidelines for the appropriate application of these models given field conditions and limited resources; (2) to incorporate the effects of surface-chemistry phenomena into reaction-transport modeling; (3) to develop methods to identify and quantify important chemical and biological reactions affecting transport of inorganic and organic substances; and (4) to compile estimates of reaction rates and reaction-rate laws for chemical and biological reactions. In addition to model development, the project undertakes field, laboratory, and theoretical studies to investigate field-scale chemical transport in groundwater and watersheds, soil CO2 flux in arid environments, isotope fractionation processes, the thermodynamics of surface complexation and other chemical reactions, and the climate record in Devil's Hole carbonate deposits.

To measure, predict, and understand the flow of water through the soil and rock of the unsaturated zone. Specifically to advance (1) knowledge of aquifer recharge rates for improved management of water resources, (2) the assessment and quantification of hazards from contaminants near the earth's surface, and (3) the understanding of soil moisture processes in relation to ecological habitat. Results are directed toward large-scale problems of water quality, water availability, land-use evaluation, and environmental impacts of climate change.

General objectives are to 1) add to the fundamental understanding of Se biogeochemistry; 2) document Se sources and assess the environmental impacts of Se contamination; 3) construct and validate an ecosystem-scale Se methodology that connects dissolved Se to bioaccumulated Se within an occurrence of Se exposure; and 4) develop scenarios to illustrate ecosystem foodwebs and hydrologic settings that control Se exposure within a watershed or site as an ecologically consistent management approach for Se. Within that framework, the specific objectives are to 1) quantitatively apply ecosystem-scale Se modeling on a site-specific basis in support of fish and wildlife management or protection through collaboration with federal and state agencies and Water Science Centers; 2) review and consult on Se monitoring and assessment plans generally for analytical adequacy and specifically as the basis for ecosystem-scale Se modeling; and 3) review habitat restoration plans and Se treatment technologies as an extension of Se remediation technologies. Application of the model focuses on Se impairment from oil refinery effluent and agricultural waste disposal in San Francisco Bay-Delta Estuary; coal waste disposal in valley fill areas of West Virginia; phosphate mining waste shale disposal in southeast Idaho; copper mining waste disposal in the Great Salt Lake, Utah; and areas of seleniferous marine sedimentary formations in California integrated with agricultural (San Joaquin Valley and San Joaquin River) and urban development (Newport Bay watershed). Several sites require defining such fundamentals as estuary interfaces and ecosystem fine-structure processes in terms of environmental Se science to provide the basis and context for site-specific modeling and scenario development. Review and consultation focuses on the San Joaquin River as an outlet for agricultural drainage containing Se; the assessment of treatment technologies for stored agricultural drainage in the western San Joaquin Valley; the Salton Sea restoration plan in terms of Se and habitat creation; and southeastern Idaho mining expansion that requires documentation and prediction of Se impacts.

My research objectives include characterization of dissolved and particulate natural organic acid influence on the reactivity, bioavailability, and mobility of metal ions and inorganic surfaces in aquatic environments. An important research objective of my project is examination of formation and dissolution rates of carbonate minerals. Biocalcification is a significant carbon sink in the world carbon budget and requires further investigation. I study aspects of biocalcification processes that proceed through a highly unstable calcium carbonate polymorph – amorphous calcium carbonate (ACC) stabilized by organic acids. I use chemical thermodynamics and kinetics to better describe and predict the fate and distribution of contaminant metal ions (for example, uranium and strontium-90) in the aquatic environment. I combine onsite field measurements and sampling, laboratory analysis and simulation, and geochemical computer modeling to support fundamental studies in geochemical kinetic processes and metal ion-natural organic acid interactions research. I study carbonate mineral formation and dissolution reaction rates and characterize the influence of natural organic acid on carbonate mineral reaction mechanisms in aqueous systems. I also examine DOA mediation of the transport and accumulation of mercury and calcium ions in aquatic systems. US Geological Survey study sites I use include: the Florida Everglades; the Sleepers River Basin, Vermont; Rocky Mountain National Park, Colorado; the Yukon River Basin, Alaska; Pyramid and Big Soda Lakes, Nevada; the Amargosa Desert Research Site, near Beatty, Nevada and the Shingobee River Headwaters Area, north central Minnesota.

This project investigates the spatial and temporal variability of ground-water surface-water exchange in response to changes in the geometry and hydrogeologic properties of this interface that are driven by episodic and sustained fluvial and hydrologic events. Episodic events are common and occur across a broad range of physical and climatic settings and are rarely accounted for in scientific investigations or resource management. Linkages between a dynamic sediment-water interface and the resulting fluxes between ground water and surface water need to be understood, quantified, and modeled to determine their influence on the quantity and quality of our Nation’s water resources as well as the ecological changes that occur at this important ecotone. Quantification of the spatial and temporal variability of these linkages across the full spectrum of fresh-water settings, including streams and rivers, lakes, wetlands, and estuaries, is required, followed by determination of the larger scale significance of these processes and linkages related to surface-water and ground-water supply, water quality, and water storage. The significance of these processes with regard to climate change also is investigated through a continuation of three decades of data collection at three long-term field sites. Hydrogeologists, geomorphologists, geochemists and ecologists conduct periodic research at these sites during multi-year and decadal-scale climate cycles ultimately to predict system responses to climate change of greater significance and duration.

Delineate and quantify processes affecting the movement and distribution of pollutants in hydrogeologic systems. (1) Determine the sorptive capacity of soil and sediment for compounds of interest that are dissolved in water; (2) identify the roles of soil and sediment organic matter and mineral components in sorption of pollutants; (3) examine the interaction of natural organic matter with mineral surfaces and its consequent effect on sorption of compounds of interest; (4) characterize the effect of dissolved organic matter on the solubility and mobility of organic contaminants in natural water; and (5) determine the characteristics of pyrogenic soil components (black carbon) and its effects on fate and transport of organic compounds.
A significant effort will be directed toward establishing the properties of pyrogenic materials in the environment. This will include both naturally occurring materials that results from fires, as well as biochars, which are produced specifically for application to soils. This research will improve the understanding of pyrogenic soil components, which have a significant effect on soil properties and soils interaction with organic compounds and other compounds of environmental significance. These pyrogenic soil components can be highly variable in properties based on their formation conditions.

Quantify the effect of aquatic and floodplain vegetation on sediment and nutrient budgets along several dimensions of hydrologic connectivity (longitudinally, laterally, and temporally) in the Difficult Run floodplain watershed; Determine if long term trends in anthropogenic nutrients are linked to improvements in submerged aquatic vegetation (SAV) diversity and abundance in other less urban estuaries, as they were in the highly urban, Potomac River; and Habitat evaluation and restoration of coastal wetlands and estuaries in the face of climate change and other stressors such as exotic species and eutrophication.

Improve our understanding of groundwater flow and transport by developing and using environmental tracers to characterize groundwater flow and transport, and by developing new methods for combining tracer analysis and groundwater model calibration.

The objectives of my research are to quantify mercury export and yields from multi-scaled watershed systems and to compare and contrast different forms of Hg (i.e. methylmercury) to understand the processes governing the dynamics of Hg transport and cycling. I also aim to determine an accurate understanding of the estimates of Hg stored in permafrost.

Characterizing Groundwater Flow and Chemical Transport in Fractured Rock From Meters to Kilometers: The objectives of my research are to develop a conceptual understanding of geologic, geochemical, and biological processes that affect groundwater flow and chemical transport in complex geologic settings, such as fractured rock and karst aquifers, and to test hypotheses under field scale conditions. Because the geologic complexity of fractured rock and karst aquifers can manifest itself differently over increasingly larger physical dimensions, the formulation of hypotheses and the design of field scale experiments are undertaken over physical dimensions that range from meters to kilometers.

The objectives of my work are to better understand nutrient sources and cycling in specific environments to aid in resource management and pollution abatement and to improve and develop isotopic analytical methodologies.

To provide useful tools in river hydraulics, sediment transport, and geomorphology that: can be used to predict the impacts of man’s activities in rivers, canals, and reservoirs; can forecast the natural evolution of fluvial courses of water; provide analytic and computational platforms to study hypothesis; and enhance our understanding of fluvial morphodynamics.

There are two major questions being addressed at study sites of this research project.
(1) To what degree is the phosphorus in sediment at a study site bioavailable?
(2) Will the phosphorus in the sediment be retained or released to the water column over time?
The objectives of my research are (1) to determine the geochemical associations of nutrients (in particular phosphorus) and metals in sedimentary environments (2) determine what these associations mean with respect to bioavailability or release of nutrients or metals to the water column. Bottom sediment is a major control over the concentrations of nutrients and metals in the water column because sediment can retain nutrients and metals or release nutrients and metals to the water column. When studying the release or retention question scenarios must include the mixing of sediment with the water column during high flow events or sediment resuspension and diffusive flux in which nutrients and metals move from high concentrations in sediment interstitial water to lower concentrations in the water column overlying the sediment. The interaction between metal oxides and nutrients can affect both the bioavailability of the nutrient or the retention-release processes in the sediment.

I am interested in landscape dynamics, generally focused on understanding and predicting changes in the patterns and functions of landscapes in response to anthropogenic effects. The objectives of my research are to gain an understanding of the processes that control landscape form and function as well and key interactions between hydrology, sediment transport, climate, vegetation, and human impacts in a variety of settings. Examination of these processes and interactions in different environments can ultimately lead to a more general and regional perspective of landscape morphodynamics and evolution. The recent research that I have initiated at USGS is a reflection of my direction and interests. I am keenly interested in sediment transport and particle residence times in varying fluvial and estuarine environments and how these change in response to human activities (such as best management practices (BMPs), dam management, and restoration activities). I am also interested in the behavior and transport of particle-associated contaminants and nutrients as a result of industrial activities, energy extraction, and agricultural and land use practices.

To study the mechanisms, pathways, and rates of transformation of carbon and nitrogen compounds (natural and contaminant) mediated by microorganisms in aquatic habitats and identify factors controlling these transformations and to examine the effect that these transformations have upon other biogeochemical processes.

Most of my current efforts are committed to multi-catchment investigations designed to distinguish the roles of vegetation, climate, and land-cover change and to put these in a hydrologic and biogeochemical framework as well as to examine ecosystem costs and services focusing on water, carbon, and biodiversity.
Two projects consume most of my efforts: (1) Work related to the Luquillo USGS Water, Energy, and Biogeochemical Budget (WEBB) Project in eastern Puerto Rico and parallel work in Panama is in the modeling and write-up phase (60% time). The objective is a comprehensive assessment of catchment hydrology and biogeochemistry in a humid-tropical landscape. In Puerto Rico we compare two rock types, quartzose and quartz-free igneous rocks, and developed versus nondeveloped. The parallel work in Panama allows comparison with igneous-forested-flat and carbonate catchments. For Puerto Rico, we (with Sheila Murphy) edited an published a nine-chapter, multi-contributor, USGS Professional Paper-1789 (PP-1789). The PP is the first comprehensive synthesis of the dataset. We now have in press, in the Owen Bricker volume of Aquatic Geochemistry, a synthesis of runoff-concentration relations. Future activities will focus on publishing additional data and models in peer-reviewed journals, the analysis of sediments collected during the project, and continued monitoring. (2) The Agua Salud Project in the Central Panama Canal Basin http://www.ctfs.si.edu/aguasalud/ examines the manifold effects of different styles of reforestation as compared to mature forested and deforested catchments (20% time). This 20-to-40 year study will assess hydrologic and biogeochemical processes both at a fine scale and at the scale of the Panama Canal Basin. The relation between processes and ecosystem services is a focal consideration. Two papers have BOA approval and are in press at this time, and to continue this work, a NSF proposal to Water Sustainability and Climate (NSF 13-535) was submitted on September 10, 2013, with the University of Wyoming in the lead.
Five other programs are ongoing (20% time): (3) biogeochemical implications of event-type processes at the hillslope to small-watershed scale, focusing on wildland fires and landslides, (4) intercomparison of soils, nutrients, and plants in forest-dynamics research plots of the global tropics, (5) biogeochemistry of the Boulder Creek Watershed, Colorado, now focusing on the effects of the Fourmile Fire and the recent floods (a major effort for Sheila Murphy), (6) continued examination of carbon sequestration in soils and sediments at a global scale, and (7) biogeochemical implications of glacial erosion. I anticipate the September 2013 floods will eventually take up a much larger fraction of time.

Develop new micrometeorological approaches and instrumentation to measure ET in a variety of challenging field settings.
Develop ET models with applications to specific locations to allow users to predict ET easily and inexpensively.
Investigate the performance of micrometeorological methods in complex terrain.
Relate changes in ET to changes in weather patterns (e.g. El Nino in a desert setting) or to changes in land use (e.g. agricultural conversion, forest thinning).
Develop guidelines for use of micrometeorological methods at limited fetch sites

My research focuses on biogeochemical cycling in freshwater aquatic ecosystems. I study terrestrial-aquatic coupling of carbon, nutrients, and major ions and organic-inorganic transformations that occur in aquatic ecosystems. My research uses newly collected data as well as analysis of existing databases such as the USGS National Water Information System (NWIS). I analyze these databases for spatial patterns in biogeochemical cycling related to land cover, climate, and anthropogenic influences as well as long-term trends in river chemistry.

Robin Stewart's research is focused on identifying and understanding processes influencing the fate and bioavailability of selenium and mercury in food webs across a range of aquatic environments including estuaries, rivers, lakes and reservoirs.

The overarching objective of my research is to integrate hydrology, pedology, chemistry, and physics to develop an improved process-level understanding of fluid, solute, and heat transport in unsaturated zones with applications ranging from geologic hazards to carbon storage in soils. I try to develop multi-disciplinary understanding of unsaturated zones in diverse settings with respect to groundwater-recharge and contaminant-transport determining processes, soil formation, and soil-water-plant-atmospheric interactions. I lead teams and work with others to generate individual and multidisciplinary synthesis products that address long-standing problems of fundamental importance to water resources, such as groundwater recharge in arid environments, impacts of land-use and climate change on water resources, surface water-groundwater interactions, and short and long-term fate and transport of disposed wastes.

Recent increases in the atmospheric concentrations of carbon dioxide and methane have emphasized the need for a more complete understanding of the processes that control carbon transfer among air, land, and water. Knowledge of the amount, rate and chemical form of carbon transfer across environmental interfaces, such as the land-air and water-air interfaces, is of particular importance. These fluxes are commonly controlled by a combination of physical, biological, and chemical processes at or near the interface. Isolation of the primary mechanisms that determine carbon transfer across the interface allows for development of process-based models that can be used for carbon mass transfer estimates at the ecosystem or landscape scale. This knowledge is also useful for prediction of the long-term effects of land- or water-use change on carbon mass transfer rates. Objectives of this project are to: characterize and quantify the carbon transfers that naturally occur across environmental interfaces, and isolate the physical, biological and chemical controls of those fluxes, evaluate the effects of environmental change on the observed interactions, and develop process based models that explain field and laboratory observations.

Our research seeks to evaluate and understand the processes that control and respond to changes in the level of CO
2 in the atmosphere. Our interests include the natural cycling of CO
2 and carbon through plants, soils, seawater, rocks, and sediments. We study the causes and effects of past geologic changes in atmospheric CO
2 levels, and the ongoing effects of human actions on CO
2 and climate.

My primary objective is to understand the function of the benthic community at various spatial scales with the goal of understanding and modeling the benthic community processes at the ecosystem level. Specifically, my goals are to (1) explore ecological and physical processes that are affected by the benthic community and that effect benthic community composition and function; (2) look at these processes at a variety of time scales (days to seasons and inter-annual time scales) so that hydrologic, climate, and exotic species effects on benthic communities and their ecosystems can be understood; (3) develop habitat and energetics models of dominant members of the benthic community that can be dynamically linked to models of hydrodynamics, phytoplankton production, and contaminant accumulation at the local and watershed spatial scale; and (4) understand and develop indices and models to describe how and when a benthic community disrupts an ecosystem (e.g. over-grazes the primary producers) and how and when a benthic community contributes to the stability of an ecosystem. All of these goals require that we understand the benthic community response to natural disturbances separate from, and in conjunction with anthropogenic disturbances such as chemical pollutants, physical alteration of water ways, restoration of habitat, and the introduction of exotic species.

Humic substances are the predominant form of natural organic matter (NOM) in soil and water and comprise the major pools of biologically refractory organic carbon and nitrogen in the biosphere. Humic substances play a role in almost all geochemical processes affecting soil and water. Knowledge of the formation and mineralization pathways of soil and aquatic humic substances is therefore critical to an understanding of the biogeochemical cycles of carbon and nitrogen, and climate change. Humic substances act as electron donor-acceptor systems and thus participate in oxidation –reduction processes with transition metal ions and biological systems in soil and water environments. Chlorination and chloramination of NOM during water treatment produces toxic disinfection byproducts. NOM binds and transports metals, and sorbs organic contaminants through both physical and chemisorption processes. Upon exposure to solar radiation, aquatic humic substances produce hydroxyl radicals that affect the cycling of iron and oxidize organic contaminants. The long term objective of my research has been to understand the structure and reactivity of humic substances, using NMR spectroscopy as a major tool, in the context of these processes.
A major emphasis has been the structure of nitrogen in NOM, and how nitrogen becomes incorporated into NOM through abiotic processes, namely through reactions with ammonia, hydroxylamine, nitrite, nitrous acid, nitrate, nitric acid, nitrogen dioxide, nitric oxide and amino acids. There is an increasing recognition of the coupled relationship of soil organic nitrogen to the carbon cycle. Concentrations of available soil organic nitrogen determine the rates of plant growth, which affects the amount of carbon dioxide plants can absorb, which in turn affects global climate. Most climate models do not take into account nitrogen and have therefore overestimated carbon uptake by plants and underestimated predicted global warming. Understanding the structural forms of nitrogen in soil humic substances, and its formation and mineralization pathways, is therefore an important goal in climate studies.
Processes of abiotic incorporation of nitrogen into humic substances are important in a number of other specific environmental problems, including the fate of atmospherically deposited nitrate in acid forest soils, the fate of nitrogenous fertilizers in agricultural soils, and hypoxia of surface waters.
Crude Oil. A major gap in our knowledge of the fate of petroleum crude oil spilled into the environment is the formation, biological refractoriness, and toxicity of the partial oxidation products of the crude oil constituents. The objective of my work at the Bemidji site is to define the nature of the nonvolatile DOC resulting from biodegradation of the contaminant crude oil, determine which crude oil constituents the NVDOC arises from, and differentiate the oil derived NVDOC from the background DOC of the aquifer.

Hydrology of Fractured Rocks:
My research objectives currently focus on characterizing the heterogeneity of fractured rock properties, and understanding the role of this heterogeneity in groundwater flow, chemical transport, and contaminant remediation. I conduct this research through methods development, field investigations, and numerical modeling. For example, recent research involves numerical modeling of multiple cross hole field aquifer tests in fractured rocks to test hypotheses about the spatial distribution of hydraulic conductivity at different scales. My research also includes collaboration on a range of topics with objectives related to contaminant characterization and remediation in fractured rocks. The overarching goal is to better understand processes affecting fate, transport, and remediation of aqueous and non-aqueous phase chlorinated compounds in fractured rocks. Since 2005, my research has been focused at the former Naval Air Warfare Center (NAWC), West Trenton, NJ, which is the Toxics Substances Hydrology Program research site for contamination in fractured rocks and is underlain by sedimentary rocks highly contaminated with trichloroethene (TCE) and its biodegradation daughter products dichloroethene (DCE) and vinyl chloride.
Model Calibration and Uncertainty:
My research in this area involves developing, adapting, and applying methods for inverse modeling and associated analyses. The objective of this research is to make advances in techniques and approaches for: constraining and calibrating groundwater models, developing field data collection strategies for improving models and their predictions, and evaluating parameter and prediction uncertainty. Even more broadly, the goals of the research are to advance how models are used for societal decision making under uncertainty.

Plan and conduct research on flow in the unsaturated zone with emphasis on development of experimental techniques and theory to describe the effects of soil physical factors, preferential flow paths, and other physical and chemical parameters of environmental importance on contamination of groundwater.

The overall objective of the MoWS research group is to gain better understanding of the precipitation-runoff processes and use this knowledge to develop improved hydrologic models. The main research topics include:
• Add functionality and improvements to the MoWS simulation models being developed and integrate with other hydrologic, hydraulic, and climate models.
• Enhance the models to use the best and latest topographic, climate, geologic, and land-use data sets as direct input to process algorithms to increase the physical nature and temporal and spatial resolution of model input.
• Develop national model structure and calibration strategy for national model application.

To elucidate and quantitatively explain the behavior of hydrogeologic systems typically characterized by hydrogeologic and physics-based complexity and data scarcity, for purposes of developing theory when needed, and with a focus on practical management (use and preservation) of water-resource systems to benefit humankind.

There are two objectives of my current research. The first objective is the generic problem of groundwater monitoring-network design. This research aims to develop statistically-sound and simulation-based methods for groundwater monitoring network design. The goal is to develop techniques that unify stochastic groundwater flow and contaminant transport simulation with optimization to develop groundwater monitoring strategies and to explore the capabilities and limitations of various monitoring-network design methods. Examples include: (1) Determining the state of groundwater and detecting or predicting changes in the groundwater environment. I am currently developing a sampling-design model for a subarea of the LA Basin using Bayesian decision analysis coupled with groundwater flow/particle tracking modeling. (2) Identifying groundwater monitoring strategies that support groundwater modeling and management. I have developed and applied a sampling-network design model for the upper Klamath Basin groundwater simulation and management models. The second objective is to develop a groundwater management framework for the upper Klamath basin that accommodates the complexities of the linked groundwater and surface water systems and accounts for the uncertainties associated with the (1) groundwater-development optimization model formulation, (2) groundwater model parameters and predictions, and (3) climate variability in the basin. The groundwater management model combines groundwater simulation and optimization to identify optimal water-resource allocation strategies under various hydrologic, water use, and regulatory scenarios; a sampling design model combines groundwater model uncertainty analysis with optimization to evaluate the worth of data and identify cost-effective groundwater sampling strategies; and a linked management and sampling design model identifies the sampling strategies that effectively reduce both modeling and management uncertainties.

1) To better understand linkages between climate (and other perturbations such as land use change and fire) and variably saturated subsurface flow with focus on hydrologically extreme environments including arid to semiarid regions and subarctic to arctic permafrost systems, and 2) to simulate/predict hydrologic and related impacts resulting from system change by integrating cutting-edge data from remote sensing and geophysical methods into innovative numerical models.

The Reaction-Transport Modeling Group provides environmental managers and policy makers with the understanding and tools needed to predict how decisions made today can improve the amount of clean water available to both society and to nature in the future. In support of the project goals, I have developed the Water, Energy, and Biogeochemical Model (WEBMOD). WEBMOD integrates the latest understanding of hydrologic processes with the full gamut of geochemical simulations available in PHREEQC to simulate conservative and reactive transport of solutes that cycle between the atmosphere, the soils, and bedrock.

The broad objective of my research is to determine rates and controls of organic carbon metabolism as a fundamental component of the terrestrial-aquatic-atmospheric exchange of carbon. I quantify the relative importance of intrinsic substrate properties and environmental variables to carbon metabolism, and the impact of climate change and other disturbances. I combine field and laboratory study approaches to understand the numerous controls on carbon cycling processes. Much of my research has focused on boreal and arctic systems, where nearly &frac12; of the global soil organic pool resides and is vulnerable to climate change. My research objectives in boreal and arctic regions include: 1) quantifying the release of carbon dioxide, methane, and dissolved organic carbon from landscapes experiencing permafrost thaw, and 2) quantifying rates and controls of the metabolism of terrestrially-derived DOC in freshwater systems of boreal and arctic regions, and the dependence on source and chemical character. This work is on-going. In addition, I have started research as part of the Water, Energy, and Biogeochemical Budgets (WEBB) program, focused on quantifying generation and loss of DOC in soils, and transport and processing of terrestrially-derived DOC in groundwater and surface waters. In particular I’m interested in better quantifying the relative importance of microbial processing vs. sorption in the removal of DOC in soils and how that may impact the quality of the DOC that reaches surface waters.

My goal is to improve the quality of groundwater modeling both inside and outside the USGS by making it easier for modelers to create models and to examine the results of those models. I do this, in part, by writing graphical user interfaces for the models. Another important aspect of my work is to provide support for modelers who have run into technical difficulties.

The geometry and pattern of river channels adjust to significant changes in the water discharge, size, and quantity of sediment supplied to the channel. When the quantity of water and sediment over a period of years remains relatively constant, the channel geometry and pattern vary about a mean of quasi-equilibrium conditions. Major watershed alterations that change the supply of water, sediment, and size of sediment reaching the channel necessitate an adjustment of the channel geometry and pattern. That is, the channel is transformed from one quasi-equilibrium state to another. Between the two quasi-equilibrium states, there is a period of instability and adjustment. The dynamics and rate of river channel adjustment during the period of instability have rarely been studied, and are rather poorly understood. The primary focus of this research project is to understand the dynamics and rate of river channel change and develop numerical models to make predictions of river channel characteristics given a particular change in flow regime and sediment supply. The greatest deficiencies in our present knowledge of river channel adjustment are (1) the longitudinal sorting of bed material, especially gravel, (2) the formation and stability of bed forms, (3) adjustment of channel width through the erosion and deposition of bank material, and (4) the rates at which the several hydraulic variables adjust. Specific objectives are to develop physically-based numerical models to describe the processes and rate at which a river channel adjusts in response to a change in the water discharge, sediment size, and sediment load supplied to the channel, emphasizing the adjustment of those aspects of river channels that significantly influence the aquatic ecosystem (that is the bed-material size distribution, occurrence of bars, and channel width); describe the hydraulic processes controlling these characteristics of river channel as well as the rate at which they function; formulate mathematical models of the processes as required for longitudinal routing of water and sediment; and develop new analytical tools for describing river-channel adjustment. For additional information on wildfire studies: seeHydrologic and Erosional Responses of Burned Watersheds.

Degradation of organic material produces organic compounds that both alter the quality of water and affect the inorganic reactions. The hydrogeologic controls on organic-inorganic reactions, their rate, and progress are not well understood. This project focuses on the occurrence and fate of organic compounds in (1) contaminant aquifers, (2) soils, and (3) lake sediments. Project objectives are to increase our understanding of reactions involving organic matter and to evaluate the significance of these reactions in geochemical studies. Of particular interest are: identifying organic and inorganic compounds that are present as a result of the degradation of organic material; studying the interaction of organic compounds with soil and aquifer materials; and using geochemical models to describe processes in organic-rich environments.

The Tropical and Arid Regions Climate Project seeks to quantify past variations in climate and the hydrologic balance through studies of paleo and modern surface- and ground-water systems using stable isotope and other chemical methodologies. Objectives of the Tropical and Arid Regions Climate Projects are to determine: (1) the frequency and severity of drought during the past 10,000 years, (2) the frequency and severity of major cooling events that led to glacial advances in the Colorado Rockies, (3) the frequency of hurricanes that impacted the Carribbean and Gulf of Mexico over the past 400 years, and (4) the impact of climate change on prehistoric Native Americans.

Metals and metalloids occur in the environment both as natural constituents of water and as contaminants. The focus of my research is to identify and develop geochemical and particularly isotopic approaches to identifying the sources, transport mechanisms and fates of those metals and metalloids, and to use these novel tracer tools to study hydrologic and biogeochemical processes in varied field and laboratory situations. Examples of current research objectives are: 1) to use isotopes of the alkaline earth elements (Ca, Sr, Ba) to determine water flowpaths and solute sources in headwater catchments; 2) to use isotopes of Cr to understand Cr transport and contaminant remediation at industrial sites and in rivers; 3) to use isotopes of the transition elements to determine sources of these metals in dust; 4) to use isotopes of Cu and Ag to assess potential isotope fractionation mechanisms in aquatic organisms as indicators of metal toxicity.

The responsible use of our Nation's ground-water resources requires an ability to predict changes in water quality as a result of human impacts. Prediction of chemical quality in the ground-water environment depends on a detailed understanding of both chemical and hydrologic processes. To determine the spatial and temporal variability of ground-water quality, it is necessary to identify reactions occurring in the system, to define their kinetic and thermodynamic properties, and to determine how the configuration of the hydrologic regime influences ground-water quality. The objectives of this project are to: (1) identify chemical reactions in ground-water systems using observed chemical and isotopic composition of dissolved solutes and minerals, (2) develop geochemical models to aid in interpretation of chemical and isotopic data from ground- water systems, (3) develop tools for age-dating groundwaters, (4) determine rates of chemical reactions in ground-water systems from field hydrochemical data and modeled water ages, (5) conduct laboratory experiment to obtain thermodynamic data for mineral- water systems for use in geochemical models, (6) obtain laboratory kinetic data on rates of mineral dissolution and precipitation for comparison with field rates, and (7) study the fundamental mechanisms of mineral dissolution and precipitation as they apply to pure phases and to solid-solution minerals. For information related to tools for age-dating ground-water, see the Reston Chlorofluorocarbon Laboratory

Many persistent organic compounds are hazardous to human and ecological health. The transport characteristics of these compounds across environmental phases are strongly influenced by adsorption and partition interactions with the individual phases. Quantification of process rates and partition constants of organic pollutants in air, water, soil, and biota is an important step in defining the level of organic contaminants in environmental systems and their potential impact on environmental quality. Project objectives are to delineate and quantify processes affecting the movement and distribution of persistent organic compounds in hydrogeologic systems. Specifically: (1) determine the sorptive capacity of soil and sediment for organic compounds in air and water; (2) identify the roles of soil and sediment organic matter, mineral components, and moisture in sorption of organic compounds; (3) establish the physical basis of bioconcentration and lipophilicity of organic compounds; and (4) characterize the effect of dissolved organic matter on the solubility and mobility of organic contaminants in natural water.

Toxic contaminants and naturally occurring substances found in the subsurface can exist in multiple phases, and undergo complex reactions including biodegradation. A comprehensive and quantitative understanding of the processes controlling the fate and transport of subsurface contaminants is necessary to develop policies and strategies for managing water-quality conditions in different land use and environmental settings. Numerical models that simulate flow, transport, and reactions are useful tools for understanding the fate of chemicals in the subsurface when used in conjunction with field and laboratory studies. The research efforts of this project consider flow and chemical behavior in the saturated and unsaturated zones. We cover a broad range of contaminants including petroleum hydrocarbons, actinides, chlorinated solvents, creosote compounds, and agricultural chemicals. Using the same basic techniques, we also conduct research on the role of groundwater flow in transporting heat and chemicals along active faults. Members of this project develop and use numerical models, conduct field studies, and perform laboratory experiments, to understand flow, transport, and reactions of chemicals in the subsurface. These chemicals can include anthropogenic contaminants as well as naturally occurring species such as nutrients, terminal electron acceptors, reactive minerals and surfaces.

The project focuses on the use of analytical techniques that we have developed to support a wide range of studies in water-rock interaction, integrating solid phase mineralogy and elemental chemistry and clay mineralogy into hydrologic and contaminant studies.

Reconnaissance and chemical and isotope sampling of thermal springs in the western United States has not generally provided information of sufficient detail to permit the geothermal potential of most individual areas to be determined with any certainty. This is especially true in the Cascade Mountain Range, where the chemical geothermometers indicate much lower temperatures of water-rock equilibrium than the sulfate-isotope geothermometer and the geologic setting seem to require. This discrepancy could be due to simple mixing of thermal and fresh water or rapid equilibration of water with the surrounding country rock as the fluids rise to the surface; alternatively, the sulfate-isotopic composition could be an artifact reflecting the original source. In this project, the origin of the dissolved constituents, water, and gases discharging in the hot springs will be investigated, their relationship to the fumaroles and cold mineral springs ascertained, and recharge areas for the thermal springs and the amount of mixing of thermal and nonthermal waters will be determined. For additional informaition, see the Dynamics of Volcano-Hydrothermal Systems web site.

Toxic contaminants and naturally occurring substances found in the subsurface can exist in multiple phases, and undergo complex reactions including biodegradation. A comprehensive and quantitative understanding of the processes controlling the fate and transport of subsurface contaminants is necessary to develop policies and strategies for managing water-quality conditions in different land use and environmental settings. Numerical models that simulate flow, transport, and reactions are useful tools for understanding the fate of chemicals in the subsurface when used in conjunction with field and laboratory studies. The research efforts of this project consider flow and chemical behavior in the saturated and unsaturated zones. We cover a broad range of contaminants including petroleum hydrocarbons, actinides, chlorinated solvents, creosote compounds, and agricultural chemicals. Using the same basic techniques, we also conduct research on the role of groundwater flow in transporting heat and chemicals along active faults. Members of this project develop and use numerical models, conduct field studies, and perform laboratory experiments, to understand flow, transport, and reactions of chemicals in the subsurface. These chemicals can include anthropogenic contaminants as well as naturally occurring species such as nutrients, terminal electron acceptors, reactive minerals and surfaces.

Advance the utility of environmental models by improving how models are tested against data and how they are used to understand simulated processes, predictions and prediction uncertainty. This includes ways of making models more transparent and refutable. Making a model transparent means that tests of model adequacy are clearly defined and conducted and the importance of different aspects of the model to predictions of interest are readily apparent. Thus, in more transparent models it is easier to determine what data and simulated processes dominate model development, predictions, and measures of prediction uncertainty. I consider sensitivity analysis to be a primary way of making models more transparent. Making a model refutable means that the model is designed such that data can be used to test specific aspects of model construction. In a more refutable model, it is more likely that model inadequacies can be readily identified. This has implications for identifying models that likely have greater predictive ability.

The ability to analyze models depends on model characteristics. More nonlinear models are more difficult to analyze. Models that are more nonlinear than the systems they intend to represent produce make it difficult to understand the actual system with its real nonlinearities and are more difficult to analyze than they need to be. An important aspect of improving models is identifying and, where possible, correcting these unrealistic nonlinearities.

Much work has been done to track spilled oil and study its fate and its effect on the environment. Our studies involved developing and applying methods to identify and track spilled oil as it weathers, as well as to differentiate it from other petrogenic hydrocarbon input sources, as well as differentiating petrogenic sources. This work in identifying petroleum sources, both natural and anthropogenic, has a great deal of transfer value to other estuarine systems.

To anticipate the effects of potential climate change (natural or anthropogenic) on hydrology and to assess hydrologic trends will require an understanding of past long-term hydrologic variability. There also is a critical need for data on extreme floods for better understanding flood processes, in engineering hydrology, flood-hazard mitigation, and other disciplines requiring flood-risk assessments. Probably the best information on hydrologic variability and extreme floods is provided by paleohydrologic and other proxy data analyzed with the help of hydrologic models. Methods for extending existing climatic and hydrologic records over long-time scales are needed. A relatively new approach, one that complements hydrologic modeling efforts, involves the application of paleohydrology to determine regional scale hydrologic variability over relatively long-time intervals (100 to 10,000 years). Existing techniques for paleohydrologic reconstruction have large errors; hence, there is a critical need to improve paleohydrologic techniques. The primary goals of this project are to (1) improve techniques to reconstruct the fluvial history of river basins, particularly for extreme floods; (2) improve the understanding of hydrologic and hydraulic processes to improve numerical models of rivers; and (3) improve the understanding of links between climate and hydrology. These goals are closely related because the development and use of paleohydrologic techniques require an understanding of geomorphic response to climate change and an improved understanding of hydrologic and hydraulic processes.

Uranium mill tailings and related forms of low-level radioactive waste contain elevated contents of naturally occurring radionuclides that have been brought to the surface, processed for the recovery of uranium and/or other components and then disposed of in near-surface impoundments. The long-term fate of the tailings and their constituents will be determined by surficial earth processes. Project objectives are to study the chemical form in which radionuclides and selected stable elements are retained in surficial earth materials, particularly uranium mill tailings, and to identify processes operating in natural aqueous and terrestrial systems that may influence the transport of these constituents from these earth materials.

Microbes are essential in contributing to and maintaining the health of aquatic ecosystems. They form the base of food webs and mediate essential biogeochemical processes, including the degradation of xenobiotic contaminants. We are conducting basic research on the microbially mediated geochemical transformations of organic and inorganic compounds in a variety of marine and freshwater environments in order to define the chemical and microbial processes that transform, degrade, or otherwise affect a contaminant's fate and transport. For additional information, see the microbiology home page for this project.

The energy potential of geothermal waters from geopressured systems is enormous. Geochemical data are necessary for delineating favorable exploration areas, estimating the recoverable geothermal resources from a given reservoir, and identifying potential pollution, waste disposal, and corrosion problems. The project's objectives are to study the chemistry and controls on the chemistry of water in geothermal and other subsurface systems; to provide basic data needed to estimate the geothermal energy and other resources; and to identify potential pollution, waste disposal, and corrosion problems associated with extraction of energy and other resources from these systems.

Ground-Water solute-transport simulation modeling is an important tool that aids in the analysis of ground-water contamination problems, both actual and potential. Accidental spills, leakage, and waste disposal operations can lead to ground-water contamination. The ability to analyze and predict the movement of solutes in ground-water systems is necessary to assess the effects of a contamination situation or properly design a waste-disposal operation. Laboratory experiments are essential to understanding geochemical reactions in the field and for obtaining the necessary reaction coefficients and rate constants used in transport models. Simulation modeling also is used to compare alternative strategies for aquifer reclamation. In some cases, the transported component of interest is thermal energy. Heat transport simulation is useful in the analysis of geothermal systems, waste heat storage systems, and some deep aquifer systems. Project objectives are to develop and apply new analytical, quasi-analytical, and numerical techniques to the field of saturated ground-water solute-transport simulation modeling; develop mathematical representations of solute-porous medium interactions and chemical reactions and develop and apply efficient algorithms for numerical calculation; apply analytical and numerical simulation modeling to laboratory and field-scale situations, both actual and experimental; and evaluate accuracy of laboratory experiments for predicting geochemical behavior of solutes in the field.

Management of ground-water resources requires that the extent and rate of movement of contaminants in the saturated and unsaturated zones be understood. The contaminants have been and will continue to be both accidentally and deliberately introduced into ground- water systems. Some of these contaminants constitute very hazardous conditions. Because of the immediacy of such contamination problems, understanding of the physical and chemical processes needs to be increased rapidly, and mathematical models derived from this understanding validated and documented. Although the basic mathematical transport models for ground-water systems have been developed, many of the parameters in these models have not been adequately investigated. A portion of this project will be devoted to increasing understanding of the factors influencing these parameters and of the interrelationship between parameters. As this understanding is developed, appropriate two-dimensional and three-dimensional mathematical models will be derived to describe contaminant movement in complex field situation including the unsaturated zone where critical. Concurrent with model derivation will be extensive study of the appropriate digital computer algorithms used to numerically approximate the solution to the transport equation.

Uranium mill tailings and related forms of low-level radioactive waste contain elevated contents of naturally occurring radionuclides that have been brought to the surface, processed for the recovery of uranium and/or other components and then disposed of in near-surface impoundments. The long-term fate of the tailings and their constituents will be determined by surficial earth processes. Project objectives are to study the chemical form in which radionuclides and selected stable elements are retained in surficial earth materials, particularly uranium mill tailings, and to identify processes operating in natural aqueous and terrestrial systems that may influence the transport of these constituents from these earth materials.

Microbes are essential in contributing to and maintaining the health of aquatic ecosystems. They form the base of food webs and mediate essential biogeochemical processes, including the degradation of xenobiotic contaminants. We are conducting basic research on the microbially mediated geochemical transformations of organic and inorganic compounds in a variety of marine and freshwater environments in order to define the chemical and microbial processes that transform, degrade, or otherwise affect a contaminant's fate and transport. For additional information, see the microbiology home page for this project.

Uranium mill tailings and related forms of low-level radioactive waste contain elevated contents of naturally occurring radionuclides that have been brought to the surface, processed for the recovery of uranium and/or other components and then disposed of in near-surface impoundments. The long-term fate of the tailings and their constituents will be determined by surficial earth processes. Project objectives are to study the chemical form in which radionuclides and selected stable elements are retained in surficial earth materials, particularly uranium mill tailings, and to identify processes operating in natural aqueous and terrestrial systems that may influence the transport of these constituents from these earth materials.

Microbes are essential in contributing to and maintaining the health of aquatic ecosystems. They form the base of food webs and mediate essential biogeochemical processes, including the degradation of xenobiotic contaminants. We are conducting basic research on the microbially mediated geochemical transformations of organic and inorganic compounds in a variety of marine and freshwater environments in order to define the chemical and microbial processes that transform, degrade, or otherwise affect a contaminant's fate and transport. For additional information, see the microbiology home page for this project.

Human activities from climate change to waste discharges to water management are modifying ecosystems across the earth, often in ways that are not well understood. This project addresses the problem of better understanding changes in aquatic ecosystems as driven by human disturbances interacting with natural processes. More specifically, the project studies a) the mechanisms of biological and ecological response to stressors such as metal contamination, nutrient enrichment, physical habitat alteration, climate change, and introduced species, and b) the influence of species, communities, and ecosystem processes on the distribution, transport, and fate of chemical contaminants (e.g., metals, nutrients). Most studies on the project ultimately consider physical, chemical and biological processes that interact in ecosystem change, as well as mechanisms of stressor-specific responses in species, populations, and communities, with an emphasis on invertebrate organisms/communities. Both intensive laboratory and field experimentation as well as long term field observation are typical of project work. An important goal is development of models to improve understanding of biological and ecological responses to stressors. For example, biodynamic models are an important focus of metal contamination studies (and studies of the implications of developing nanotechnologies) because they provide a mechanistic explanation of many biological and ecological responses to metals. These models are based upon laboratory-based experimental studies of contaminant uptake, loss and detoxification in different species linked to field observations of contaminant concentrations. Understanding differences in contaminant biodynamics, when linked with carefully designed studies of benthic communities, for example, can lead to process-based predictions of ecological change. Ongoing or past project includes studies in streams, rivers, lakes and estuaries. Historically, the project has introduced many new methodologies. Continued refinement of those and the development of novel new methods is another important ongoing and future goal of this project. Perpetuation of long-term (multi-decadal) ecological, metal and geochemical data sets, in collaboration with non-USGS partners, is also an ongoing goal in ecosystems from South San Francisco Bay, North San Francisco Bay, Santa Clara Valley streams, and the Clark Fork River Montana. The unique capacity to integrate laboratory and field studies across levels of biological organization in diverse aquatic ecosystems establishes our ability to identify, tackle, and inform managers and scientists of newly emerging issues which is a critical need of the USGS and an important part of our work into the future. For additional information, see Ecology and Contaminants site.

Reconnaissance and chemical and isotope sampling of thermal springs in the western United States has not generally provided information of sufficient detail to permit the geothermal potential of most individual areas to be determined with any certainty. This is especially true in the Cascade Mountain Range, where the chemical geothermometers indicate much lower temperatures of water-rock equilibrium than the sulfate-isotope geothermometer and the geologic setting seem to require. This discrepancy could be due to simple mixing of thermal and fresh water or rapid equilibration of water with the surrounding country rock as the fluids rise to the surface; alternatively, the sulfate-isotopic composition could be an artifact reflecting the original source. In this project, the origin of the dissolved constituents, water, and gases discharging in the hot springs will be investigated, their relationship to the fumaroles and cold mineral springs ascertained, and recharge areas for the thermal springs and the amount of mixing of thermal and nonthermal waters will be determined. For additional informaition, see the Dynamics of Volcano-Hydrothermal Systems web site.

Sediment moves through a river system in response to specific events and changing conditions in the drainage basin. The movement of sediment is usually discontinuous. Episodes of movement are separated by periods of storage that can range from less than a year to more than one thousand. Understanding the movement and storage of sediment in rivers is important to navigation, flood control, and other aspects of river engineering, as well as to the prediction of the fate of contaminants adsorbed on sediment particles. This project's objectives are to assess: (1) changes in river sediment loads over periods of decades or longer, and the factors (natural or artificial) that cause the changes; (2) rates at which sediment is stored in river systems and the residence times of sediment particles in storage; and (3) sources, pathways, and sinks of sediment particles in river systems.

Stable and radioactive isotopes such as oxygen, hydrogen, carbon, nitrogen and sulfur have proved to be extremely useful tracers of hydrologic pathways, biogeochemical processes, and residence times of waters and solutes. However, use of these isotopes as tracers is presently hampered by our limited understanding of the physical processes and chemical reactions influencing isotopic compositions. The unsaturated zone, particularly the soil zone and the top of the water table, is probably the portion of the hydrologic system most responsible for alteration of the isotopic compositions of potential isotope tracers, this environmental component is also one of the least studied. The overall goal of this project is to increase our understanding of reactions involving stable isotopes and to evaluate the significance of these reactions in geochemical and hydrologic modeling. This will be accomplished by field and laboratory investigations of processes and reactions which may fractionate isotopes and affect their utilization as tracers of processes, flowpaths, and sources of water and solutes. For additional information related to isotopes, see the
Isotope Interest Group Home page

Efficient management of ground-water aquifers and geothermal reservoirs requires accurate estimates of the hydraulic properties of water-bearing formations. These are needed to predict water- level changes, aquifer storage capacity, and the rate of movement of chemical species or thermal energy. Analytical models, properly applied, can often be used to estimate the hydraulic and transport properties of complex aquifer systems. This project's objective is to obtain analytical solutions to specific problems of flow and transport in water- bearing formations that can be used for evaluating the hydraulic and transport properties of aquifers and geothermal reservoirs.

Geophysical data are recorded for water wells and test holes, but interpretation is subject to significant uncertainties. The data are used in ground-water models to evaluate potential waste disposal sites and the effects of ground-water contamination and to guide development of aquifers, including geothermal reservoirs. The development of quantitative log-interpretation techniques to derive more accurate data and to evaluate the statistical uncertainty in the data will reduce costs in ground-water investigations. Project objectives are to (1) evaluate presently available logging equipment and log-interpretation packages and develop improved instrumentation and analytical techniques for specific ground-water problems such as site selection and monitoring for disposal of radioactive, municipal, and industrial wasters, improve log derived estimates of physical properties, such as porosity values, (3) relate the log character of fractures to their hydraulic conductivities, (4) develop the capability of making quantitative interpretation of borehole gamma spectra, and (5) perform statistical analyses of the magnitude and sources of errors in log-derived data.

The acquisition and meaningful interpretation of sediment data from areas disturbed by land-use activities or natural processes are two of the most deficient areas of recognizing nonpoint-source pollution in the United States. The comparison of sediment data from disturbed and undisturbed areas provides a means to (1) evaluate the effects that land-use activities cause, (2) investigate the geomorphic processes that regulate the detachment and transport of sediment, and (3) develop strategies for remedial action to reduce excessive sediment discharges. This information is especially necessary to minimize sediment discharges and sorbed chemical loads from surface-mine, industrial, agricultural, and urban areas. Objectives of this project are to (1)evaluate the extent and utility of sediment data from a variety of land-use areas, (2) predict the movement of sediment from drainange basins affected by those land uses, and (3) assess existing techniques and develop new ones based on geomorphic principles and the application of statistics, geochemistry, and botany to the limited data available as aids in improving our interpretive capabilities.

The responsible use of our Nation's ground-water resources requires an ability to predict changes in water quality as a result of human impacts. Prediction of chemical quality in the ground-water environment depends on a detailed understanding of both chemical and hydrologic processes. To determine the spatial and temporal variability of ground-water quality, it is necessary to identify reactions occurring in the system, to define their kinetic and thermodynamic properties, and to determine how the configuration of the hydrologic regime influences ground-water quality. The objectives of this project are to: (1) identify chemical reactions in ground-water systems using observed chemical and isotopic composition of dissolved solutes and minerals, (2) develop geochemical models to aid in interpretation of chemical and isotopic data from ground- water systems, (3) develop tools for age-dating groundwaters, (4) determine rates of chemical reactions in ground-water systems from field hydrochemical data and modeled water ages, (5) conduct laboratory experiment to obtain thermodynamic data for mineral- water systems for use in geochemical models, (6) obtain laboratory kinetic data on rates of mineral dissolution and precipitation for comparison with field rates, and (7) study the fundamental mechanisms of mineral dissolution and precipitation as they apply to pure phases and to solid-solution minerals. For information related to tools for age-dating ground-water, see the
Reston Chlorofluorocarbon Laboratory

My research is concerned broadly with the use of stable isotopes, primarily hydrogen, carbon and oxygen, to examine the dynamics of hydrological systems and associated geochemical problems. I perform studies in the identification and quantification of ground-water recharge, discharge, surface-water/ground-water interaction, redox processes in contaminated aquifers, as well as source identification of stray methane gas in drinking water wells. I develop new sample- preparation techniques in the laboratory including inlet systems for continuous- flow isotope- ratio analytical techniques , such as EA, TC/EA, GPI, Gasbench, GCC, TC/GCC, and TIC/TOC and publish Sandard Operating Procedures in the U.S. Geological Survey Techniques and Methods.

The overall objective of this project is to determine the nature of natural organic carbon and organic nitrogen during its biogeochemical cycling through the environment and its interactions with anthropogenic compounds. Emerging techniques in liquid chromatography/mass spectrometry, liquid chromatography/tandem mass spectrometry, infrared spectroscopy and other means will be used to gain new insights into dominant processes responsible for fate, transport, and reactivity. Field- and laboratory-based experiments will enable direct application to current environmental problems such as disinfection byproduct formation potential, long-term effects of forest fires, and sustainability of agricultural soils. The chemical, biologic, and hydrologic processes that produce and alter anthropogenic and natural organic carbon and nitrogen in water will be investigated as relevant to environmental problems. This project will address major questions such as how nitrogen incorporates into natural organic matter and its fate in the degradation of natural organic matter. Interdisciplinary studies will be conducted with colleagues to determine significance and mechanisms of nitrogen fate in natural organic substances in river systems. New sources of dissolved natural organic carbon and nitrogen include large-scale application of biochar to agricultural soils to increase soil organic carbon, fertility, and crop production along with long-term natural terrestrial carbon sequestration.

Temperature and salinity are two key estuarine habitat variables. Understanding how these variables are distributed around the bay leads to a better understanding of habitat types and distribution in the Bay. Additionally, understanding the distribution of salinity in the Bay allows us to better understand the transport processes that drive material transport and supply throughout the Bay. Time series of water temperature and specific conductance (salinity is calculated from conductivity and water temperature) are needed (1) to improve our understanding of the hydrodynamics of the estuary (e.g., gravitational circulation), (2) for calibration of multi-dimensional flow and transport models of the Bay, (3) to better understand the distribution of physio-chemical habitat types throughout the Bay , and (4) to provide supporting data for numerous estuarine studies of the Bay and Delta. The objective of this work is to measure the spatial and temporal variability of salinity and temperature in San Francisco Bay.

Ground-Water solute-transport simulation modeling is an important tool that aids in the analysis of ground-water contamination problems, both actual and potential. Accidental spills, leakage, and waste disposal operations can lead to ground-water contamination. The ability to analyze and predict the movement of solutes in ground-water systems is necessary to assess the effects of a contamination situation or properly design a waste-disposal operation. Laboratory experiments are essential to understanding geochemical reactions in the field and for obtaining the necessary reaction coefficients and rate constants used in transport models. Simulation modeling also is used to compare alternative strategies for aquifer reclamation. In some cases, the transported component of interest is thermal energy. Heat transport simulation is useful in the analysis of geothermal systems, waste heat storage systems, and some deep aquifer systems. Project objectives are to develop and apply new analytical, quasi-analytical, and numerical techniques to the field of saturated ground-water solute-transport simulation modeling; develop mathematical representations of solute-porous medium interactions and chemical reactions and develop and apply efficient algorithms for numerical calculation; apply analytical and numerical simulation modeling to laboratory and field-scale situations, both actual and experimental; and evaluate accuracy of laboratory experiments for predicting geochemical behavior of solutes in the field.

The determination of inorganic constituents and their impact on water quality requires an in-depth knowledge of the interactive water chemistry relationships. The ability to measure trace and ultratrace concentration levels of inorganic constituents as well as their chemical form and speciation plays a significant role on the chemical, toxicological, transport and overall environmental impact on surface- and ground-water hydrology. The development of state-of-the-art analytical chemistry technology to the solution of specific hydrologically related problems requires extensive laboratory and field research and development effort. Project objectives are to (1) Investigate and develop new concepts and approaches to the identification and measurement of inorganic constituents in water and water related materials; (2) Formulate techniques for the utilization of new field and laboratory technology for the assessment of water quality; and (3) Participate in multi-disciplinary research programs providing expertise in the field of inorganic water chemistry.

Uncertainty in application of physically based surface-water hydrologic models is a function of adequacy of the conceptualization of the processes involved and of the quantity and quality of data available to use as input to the model. In any type of modeling exercise, even if the physical processes are well understood, spatial heterogeneities make application of the model on a basin-wide scale problematic, and it is almost always necessary to use some form of spatial averaging to obtain 'effective' input variables. The over-all goal of our research is to investigate: (1) Model output errors as a function of model complexity and uncertainty in model input, (2) Derivation of simplified yet physically based models that are appropriate to use with limited data, (3) Ways of evaluating and coping with uncertainty caused by spatial variability of input variables. This project seeks to develop unified approach to analyzing and partitioning errors in hydrologic modeling with particular attention to scale and spatial averaging problems, develop improvements to existing practices, and develop new approaches to managing error levels within the constraints of reduced budgets.

Various processes within the unsaturated zone affect ground-water availability and portability, as well as concentrations of water vapor and trace gases in the atmosphere. The rate at which precipitation or applied irrigation water infiltrates, its redistribution following infiltration, and the partitioning of the redistributed soil moisture between ground-water recharge and evapotranspiration affect the rate at which the ground-water reservoir is replenished and the degree to which ground water might be contaminated by chemical applications, spills, or disposal. Consequently, knowledge of and methods to quantitatively measure and predict these processes are needed to determine the impact of such societal practices as irrigation development for agriculture, the use of agricultural chemicals, and the disposal of radioactive and/or hazardous waste in the unsaturated zone on both the availability and potability of ground water. Processes governing transport in the unsaturated zone gas phase are also important in determining the potential for ground- water contamination by volatile compounds, the rate at which water is returned from soil moisture to the atmosphere as vapor, and the fate of other "greenhouse gases", such as carbon dioxide, methane, and chlorofluorocarbons (CFCs). An understanding and quantification of these processes is needed both to assess the hazards of ground-water pollution and to better predict the impact of global change on future climate.

Natural organic polyelectrolytes are highly active materials that are present in practically all natural water systems. They interact with both organic and inorganic pollutants and nutrients, influencing, and in many instances, controlling the toxicity, rate of movement, persistence and rate of degradation of the pollutants and nutrients in aquatic environments. Detailed knowledge of the chemistry of natural organic polyelectrolytes is therefore of primary importance in understanding the chemical changes that affect all of the components of natural water systems. Organic polyelectrolytes are partially eliminated from drinking water by coagulation and chlorination; however, the products of chlorination are not known. Both natural and synthetic organic compounds are present in all natural waters. Some of these compounds are toxic or mutagenic and it is therefore important that they be identified and quantified in surface and ground water and in precipitation. Objectives include (1) isolation of the various organic polyelectrolytes present in natural water systems from different environments; (2) determination of the physical and chemical properties of the most abundant organic polyelectrolytes; (3) elucidation of the mechanisms of interaction of pollutants with natural organic polyelectrolytes; (4) elucidation of the mechanism of interaction of natural organic polyelectrolytes with mineral surfaces; (5) development of nuclear magnetic resonance (NMR) spectroscopic methods for the characterization of humic substances; (6) determination and characterization of selected organic pollutants in ground water; (7) elucidation of the mechanisms of humification in natural systems; (8) identification of diagnostic NMR bands of different functional groups found in natural organic polyelectrolytes; (9) characterization of the nitrogen containing species in natural organic polyelectrolytes; and (10) identification of the carbohydrates in humic substances.

Water quality and pollution contamination depend strongly on geochemical processes involving reactions with mineral surfaces and substrates. Such processes include weathering reactions that contribute dissolved chemicals, sorption that removes aqueous species, and electron transfer mechanisms that establish redox conditions. Although extensive research has been conducted on the aqueous chemistry, minimal information exists on the corresponding solid phases and their effects on chemical transport. Objectives of this project are to: investigate the composition and structure of common mineral surfaces and determine the extent of heterogeneity between specific surfaces and the bulk mineral phase; determine the mechanism and rates of chemical and electron transfer between mineral substrates and surface- and ground-water systems; determine the nature and extent of temporal changes in surface compositions during natural weathering and contaminant introduction and assess the effects on sorption and retardation; assess environmental hazards due to the weathering of toxic materials contained in natural minerals and rocks and plan mitigation and cleanup under geologic constraints; and assess the effects of hydrologic parameters on rates of chemical weathering in soil profiles and watersheds and predict impacts of climate change. This project also conducts studies related to the biogeochemistry of selenium; for additional information, see the
Linking Selenium Sources to Ecosystems web site.

Reconstructions of continental paleoclimates of the Pleistocene Epoch have relied almost exclusively on packrat midden, lacustrine, and speleothem records. The isotopic (deuterium, oxygen-18, carbon-13) record of calcitic veins marking the sites of fossil ground-water discharge, have not been utilized. Preliminary work indicates that such veins contain continuous dateable records of Pleistocene paleoclimate and paleohydrology. The paleohydrologic interpretations should also be pertinent to selection of sites for the disposal and long term isolation of toxic wastes. Project objectives are: (1) infer paleoclimate and paleohydrology of selected regions based on variations in isotopic content of calcitic veins of ground water origin; (2) attempt correlation of inferred local variations in continental paleoclimate with global variations deduced from marine sediment and polar ice core studies; (3) differentiate between, and determine relative magnitude of, summer and winter recharge to major uplands.

Movement of toxic and radioactive substances in aquifer systems occurs in all three phases and is controlled by both hydrologic and chemical forces. Solute movement can be greatly affected not only by physical dispersion, but by other factors such as exchange sorption, chemical kinetics, and ionic distributions. Movement of gases and particulate material in the unsaturated zone are controlled by many additional factors. Knowledge of how these physical and geochemical factors affect prediction of movement of toxic and radioactive wastes is only generally known for ideal systems. This project's objective is to develop field methods and techniques that will yield values for physical and geochemical factors of regional significance in a ground-water system.

Technical solutions to the problem of investigating and managing waste movement and disposal in regulated rivers, estuaries, and embayments require qualitative and quantitative assessment of the interactions between waste constituents undergoing dynamic transport. Mathematical, numerical, computer-simulation models offer one very powerful solution. Because water is both the vehicle by which the waste constituents are transported and the media in which the constituent interactions occur, the temporal and spatial variations of the flow appreciably govern the interactions both qualitatively and quantitatively. Design of the desired simulation models depends in large measure upon accurate mathematical/numerical representation of the hydrodynamics of the transient flow process. The broad objectives of this study are to thoroughly explore the hydrodynamics of one, two, and three-space dimensional transient flows in waterways and waterbodies (including the transport and interaction of constituents), and to develop the mathematical/numerical techniques with which to simulate these processes. The ultimate goal is to provide the hydrologist with a simulation system comprised of rational mathematical/numerical models with which to evaluate the effect of past, present, and projected changes in prototype waterbody systems.

The project focuses on the use of analytical techniques that we have developed to support a wide range of studies in water-rock interaction, integrating solid phase mineralogy and elemental chemistry and clay mineralogy into hydrologic and contaminant studies.

Natural water systems provide a wide range of conditions within which to examine the geochemical behavior and cycling of trace elements and nutrients relative to hydrochemically important mineral reactions. Processes of mineral dissolution, alteration and genesis exert strong controls on the concentrations of chemical species in natural water systems and thus on water quality. Chemical composition of atmospheric precipitation input to terrestrial watersheds affects mineral reaction rates and may regulate reaction pathways and products. Knowledge of the geochemical behavior and cycles of major elements, trace elements, and nutrients is essential in order to understand and predict the consequences of deliberate or accidental anthropogenic additions of these substances to the environment. Objectives of this project are: to define the role of mineral-water interactions in determining the chemical composition of natural waters with emphasis on major elements, trace elements and nutrients; to quantitatively describe the geochemical behavior of these species in fresh-water, estuarine and marine environments; and to assess the impacts of anthropogenic contributions on natural cycles in these systems and to evaluate the hydrogeochemistry of major elements, trace elements and nutrients as it relates to water resource utilization.

Bricker

Edward Callender

Sedimentary Geochemical Processes Affecting the Exchange of Nutrients and Transition Metals Between Sediment and Water in Riverine, Estuarine, and Lacustrine Environmentsshow detailsView Publications

Benthic sediment exchange processes are potentially a very significant source/ sink of nutrients and metals within an aquatic system. Too often the quantitative effects of these processes are only estimated when considering biogeochemical cycling and ecological responses. Understanding geochemical processes that control nutrient and transition metal chemistry of natural waters is requisite for predicting the effects man-induced events will have upon natural geochemical cycles and for determining their utilization as a natural resource (e.g. estuarine waters as food resources). Objectives of this project are to (1) study the important geochemical processes affecting the nutrient and metal composition of and exchange between sediment and water in several different aquatic environments;(2) aid in developing useful methods for determining nutrient and metal fluxes between sediment and water; and (3) assess the influence man's activities exert on their natural geochemical cycles.

Many difficult problems in river mechanics may have stemmed from inadequate understanding of the multiplicity and interaction of fluvial processes. Some of the problems may have been solved, but in a very simplified, approximate way. Many efforts have been directed, but without apparent success, to fully account for the causes, occurrences, and mechanisms of catastrophic events, such as flash floods, debris flows, and channel changes resulting from torrential storms, sudden snow or glacier melt, dam break, volcanic eruptions, and earthquakes. Such failures may be partially attributed to the deficiency and incompleteness of existing empirical formulas (or models) representing the relationships between various processes and responses. Project objectives are to seek a full understanding of various fluvial processes on hillslopes and in river channels, which undergo changes in response to rapid disturbances, such as torrential storms, sudden snow or glacier melt, dam break, volcanic eruptions, and earthquakes; improve or generalize existing empirical formulas that do not accurately describe the process- response relationships.; develop new relationships for various soils and highly-concentrated sediment-water mixtures, such as those posed in the form of rheological or constitutive equations; build mathematical models, using such relationships, for flash floods, debris flows, channel changes, etc; and ultimately apply these models to minimize the loss of life and property that may result from such catastrophic events

The ecosystem of a tide-affected estuary consists of an extremely complicated balance of natural processes and human induced activities. Some of the basic characteristics of such a system, for example the San Francisco Bay estuarine system, are not well understood. A comprehensive description of the hydrodynamics and the related transport phenomena is still lacking. A better understanding of the effects among the interactive natural and human induced processes on this system requires advances in basic science relating the physical, chemical and biological estuarine processes. Circulation in a tidal estuary is generated in response to astronomical tides, inflow of fresh water, winds, and stratification due to salinity. The basin topography (bathymetry), air-water interaction, water sedimentation interface, mixing characteristics, frictional loss at the bottom, and the rotational effects of the earth, together with the above mentioned driving forces, constitute an extremely complicated balance that conserves mass, momentum, energy, and conservative solutes in the system. Objectives are to understand processes and rates by which water, salt, and other solutes interact; develop methods to enable quantification of the relative importance of river inflow, winds, tides and other dynamic forcings that act upon the system; and develop and verify conceptual and numerical models of these interactions. For current information about work being done by this project, see project's home page.

Adequate description of mass transport in hydrologic systems requires knowledge of the rates of the reactions among the gaseous, solid, and liquid phases present. This knowledge of reaction rates is necessary because many chemical reactions occur simultaneously in natural systems, and only a few of these appear to reach equilibrium, even after long contact times. Therefore, a complete description of the chemical processes and their rates will allow realistic modeling of mass transport in natural and perturbed hydrologic systems. The objectives of this project include determining the relative importance of the factors controlling water quality and devising experiments to quantify the process by studying two model systems representing single lithologies extrusive volcanic and shale; determining the kinetics and mechanism(s) of these processes and the effects of natural variation on the controlling factors; and suggesting reaction models by combining solution chemistry and the results of surface alteration studies.

Satisfactory formulations and solutions of equations approximately describing (1) movement of fluids and components contained in fluids through consolidated and unconsolidated rocks, and (2) interactions of the fluids and rocks accompanying fluid movement, are needed for proper understanding and management of ground-water resources. Such formulations and solutions of equations that apply for general field situations where the flow system is complex and hydrologic data are inexact are not, in general, available. Project objectives are to: (1) reformulate where necessary, the equations describing the flow of fluids through porous or fractured rock to include stochastic processes, emphasizing equations that are suitable for field use; (2) derive methods to solve for dependent variables and estimate parameters in the equations; (3) derive methods to assess the uncertainty of both the results computed using the model formed by the basic equations and the parameters estimated for the model; and (4) derive methods to assess the predictive capability of the model.

In recent years, there has been increasing interest and study concerned with the possible relations between the chemical quality of natural waters and human health and disease. Medical researchers recognize areal patterns of health and disease in the U.S. and suspect that these patterns may be controlled by both environmental and non-environmental factors. After excluding non- environmental factors, it appears that local and regional differences in water quality may have an effect on health and disease. Such differences influence the total dietary intake of necessary major and trace elements and the concentration of certain potentially toxic chemical constituents. The objective of this project is to discover and quantify relationships between the chemical quality of natural waters and human health and disease. For information on additional projects in the National Research Program, see Indexes to NRP projects and bibliographies.

Understanding the effects of climatic variability is important to development of water resources, mitigation of flood hazards, and interpretation of geomorphic surfaces. Climatic variability, which is characterized by temporal changes in variability of seasonal climate that spans decades or centuries, may be more important to water-resources evaluations than changes in mean climatic conditions. Changes in variability of climate has a large effect on the probability of occurrence of extreme events, such as floods or droughts. Understanding of climatic variability and its effect on the landscape is of paramount importance for estimation of flood frequency, sediment transport rates, and long-term watershed and channel changes. The objectives of this project are to define historic climatic variability in the western United States over the past century, to identify specific time periods of statistically stationary precipitation, discharge, flood frequency, and sediment transport, to assess the net effects of climatic variability on watershed conditions and fluvial systems, and to determine the extent that historic changes reflect Holocene climatic fluctuations. See Changes in Riparian Vegetation in Arizona for examples of how repeat photography has provided an invaluable record of changes in the riverine environment. Also see Mojave Ghost Town for repeat photography documentation of vegetation recovery in Mojave Desert areas that were settled in the late 19th and early 20th century and later abandoned.

Release of various synthetic organic compounds to the environment has caused soil and ground-water pollution in many places. The processes which control the persistence and movement of these materials are not well understood. A better understanding is necessary to aid in construction of models to predict movement and fate of pollutants in the subsurface and for design of control and abatement techniques. Project objectives are to determine the transformation pathways of selected organic compounds using a combination of field observations and laboratory simulations of environmental conditions; assess the relative importance of physical, chemical, and biochemical processes in the transformation of these compounds under ambient conditions; and study relevant biotransformation processes occurring in the subsurface.

The intrusion of industrial, agricultural and domestically produced organic chemicals and wastes into the aquatic environment is a well known reality and is considered to be one of the most important environmental problems. The widespread finding of these anthroprogenic substances, in addition to naturally occurring organics, and their detrimental impact on the Nation's water resources points to our need to understand how these substances act and react in the environment. Knowledge of transport, persistence, transformation, solubility, sorption, and reaction kinetics is needed to determine the fate of the substances in the hydrosphere. Objectives of project are to (1) identify organic substances associated with the field problem, in aqueous and non- aqueous condition, sorbed and in the unsaturated atmosphere; (2) chemically determine any biotic and/or abiotic degradation or transformations occurring in the field; (3) measure sorption and reaction equilibria and rates within the aqueous system and at the water-mineral interface, using both field observations and laboratory simulations; and (4) determine the behavior of organic solutes and vapors in the unsaturated zone.

Saline hydrologic systems provide a wide range of conditions within which to examine hydrochemically important mineral reaction (alteration or genesis) and to better define reactants and products controlling the chemical composition of many natural waters. The effects of complex reactions, in addition to simple solution and hydrolysis, are reflected in relatively gross chemical change and interaction with fine-grained sediment. The objective of this project is to use saline environments to determine mechanisms and relative importance of mineralogic processes which influence the solute composition of natural waters.

The regional nature of hydrologic processes is generally defined in terms of shared meteorological and basin characteristics. Inferences have been attempted by regressing the parameters of hydrologic interest against these characteristics. Such analyses have not been able to fully explain the variations, extremes or persistence of discharge patterns observed within a geographic area. An accounting of anthropogenic effects on basin characteristics needs to be made. Longer term influences such as decadal to centennial, and millennial climatic fluctuations need to be considered, and the stochastic structure of the hydrologic process itself needs to be studied. The objectives of this project are (1.) to develop secular regional statistics for observed and proxy hydrologic variables, (2.) to use statistical methods to study the influence of climate forcing in such statistics, and identify the effect of long term climatic fluctuations on the nature of hydrologic persistence, and (3) to develop an improved understanding of regional hydrological processes as part of the global hydrologic cycle and its interaction with global climate.;For additional information about the project's collaborative paleoclimatic work see ' A Devils Hole Primer '.;For information about the HCDN (Hydro-Climatic Data Network), see USGS OFR 92-129.

Modeling of watershed response to normal and extreme climatic conditions or to changes in the physical conditions of a watershed requires the simulation of a variety of complex hydrologic processes and process interactions. Some of these processes are well understood at a point or for a small area; others are poorly understood at all scales. Increasing spatial and temporal variability in climate and watershed characteristics with an increase in watershed area adds significantly to the degree of difficulty in investigating and understanding these processes. Research is needed to better define these processes and to develop techniques to simulate these processes and their interactions at all watershed scales. Project objectives are to investigate watershed hydrologic processes and processes interactions to (1) Improve understanding of watershed system dynamic; (2) develop computer models to simulate and evaluate the effects of various combinations of precipitation, climate, and land use on streamflow, sediment yield, and other hydrologic components; and (3) develop procedures and techniques to estimate model parameters using measurable watershed and climatic characteristics. A GIS grapical-user-interface to be used in watershed modeling. for the development of Parameter Inputs for Watershed Modeling, and the Modular Modeling System, a framework which allows the model user to selectively couple to selectively couple the most appropriate process algorithms from applicable models to create an "optimal" model, see project's home page.

Although a major effort has been made to understand the hydrodynamics of surface waters, less effort has been devoted to the study of transport mechanisms and to the development and validation of computational models for simulating the transport of dissolved and suspended materials. Recent progress in hydrodynamics has created additional opportunities for advances in surface- water transport. It may be possible to develop and validate more physically correct descriptions of transport processes in terms of flow characteristics than have been previously available. Microscale processes must be expressed at the macroscale level by algorithms which can be validated in computational models using laboratory and field data. The objectives of this project include: (1) the evaluation of existing methods and techniques; (2) the development, or validation, or both, by the use of laboratory and field data, of algorithms describing dissolved- and suspended-material transport processes; (3) the development, or validation, or both, of computational techniques for solving the partial-differential equations describing surface-water transport processes; (4) the development and validation of multidimensional, computational models for the transport of dissolved and suspended materials in surface waters; and (5) the development of techniques for the application of computational, surface-water transport models to field problems.

A disproportionate amount of research in water chemistry has been directed towards defining trace levels of organic contaminants in water whereas the structures and characteristics of natural organic substances, in the dissolved, suspended, and bed sediment phases, are very poorly understood. A better knowledge of the nature of natural organic substances in water is essential to the advancement of many diverse sciences, such as organic geochemistry, aquatic biology, soil science, hydrology involving contaminant transport, and even atmospheric chemistry involving carbon cycle research. The Water Resources Division is conducting significant research on the nature of humic substances in water, which comprise less than one-half of the total organic carbon in water; a comprehensive study of the entire suite of compound classes comprising natural organic substances has been lacking. Objectives are to conduct comprehensive organic analyses of various surface-water samples where comprehensive analyses is defined as "state-of-the-art" organic analyses on as many classes (humic substances, lipids, proteins, carbohydrates, etc.) as possible within the time and resource limitations of the project; develop chromatographic, selective extraction, and derivatization methods for organic substance characterization by infrared, nuclear magnetic resonance, and mass spectrometric methods; define the chemical, biologic, and hydrologic processes which both produce and diagenetically alter natural organic substances in water; and conduct interdisciplinary studies with colleagues to determine significance and mechanisms of contaminant binding with natural organic substances.

Microorganisms catalyze most of the natural redox reactions involving carbon, sulfur, nitrogen, and metals. Thus, geochemical models of the distribution and fate of natural and contaminant compounds must include a microbiological component, which requires an understanding of the physiological characteristics of microorganisms that control the rate and extent of microbially- catalyzed reactions. Project objectives are: (1) to quantify the rates of microbial processes that influence the geochemistry of surface-water and ground-water aquifers; (2) to determine the physiological characteristics that control the rate and extent of microbial processes; and (3) to develop mathematical models of the distribution of microbial processes in surface-water and ground- water.

Greater than 90 percent of the organic solutes in water are of natural origin, yet little is known about the chemistry or source of these organic materials. However, these substances are known to complex trace metals, to transport pesticides, to be precursors of carcinogen compounds upon chlorination, and to be a food source for aquatic organisms. These processes need further clarification and quantification. The overall objectives are to quantify and to identify organic solutes that affect water quality processes. Specific objectives are: (1) to measure the amount of different organic solutes in various hydrologic environments; (2) to understand the origin, structure, and reactivity of aquatic humic substances; (3) to predict the processes which affect the fate and movement of organic solutes in surface and subsurface environments; and (4) to elucidate the roles of natural organic solutes in water purification: reverse osmosis, chlorination, activated charcoal, and ozonation.
F

Dams have been built in this century that impound virtually all major rivers in the United States. The purposes vary and include flood control, navigation, hydropower generation, and storage for irrigation and domestic uses. About 2,500 reservoirs of 5,000 acre-feet or more, store about 480 million acre-feet, about 1/4 of the annual runoff. Storage capacity is dominated by large reservoirs such that the 600 largest store more than 90 percent of the total. Lake Powell, behind Glen Canyon dam, stores water (ca. 27 million acre-feet) in the Upper Basin of the Colorado River for controlled release according to the Colorado River Compact (8.23 million acre-feet per year) and to generate electricity for sale to consumers in the Southwestern United States (about 80 percent of the generating capacity of the Colorado River Storage Project). Phenomena that control the quantity (evaporation, losses to ground water, consumptive uses in the basin, regional drought or El Nino effects, and so forth) and (or) quality (salinity , productivity, sediment-water column exchange, etc.) of Lake Powell waters are not understood. Specific objectives of this project are to initiate investigation of basic processes that mediate water quality in Lake Powell and to couple understanding of Lake Powell to management of water quality of the Colorado River in the Grand Canyon National Park.

Aquatic humic substances and other classes of dissolved organic material present in natural waters can control the biogeochemistry of trace metals and other solutes and can influence ecological processes in lakes and streams. The nature and reactivity of the dissolved organic material is in turn influenced by biological, chemical, and physical processes occurring in the aquatic environment. Recent advances in isolating and characterizing different fractions of the dissoloved organic carbon (DOC) and in measuring rates of microbial processes can be used to advance the understanding of the dynamic relationship between aquatic biota and dissolved organic material and trace metals in different environments. Project objectives are to (1) determine the processes involved in the biogeochemistry of dissolved organic material and selected trace metals in several aquatic environments; (2) describe the temporal and spatial dynamics controlling the concentration and chemical speciation of trace metals and DOC in aquatic environments; and (3) quantify carbon flux and other ecological processes involving dissolved solutes in aquatic ecosystems over a range of spatial and temporal scales.

Many aspects of ground-water flow and transport resist standard, deterministic modeling techniques: either there exist elements which are overly complex or which are simply unpredictable. These elements may have either a spatial character, as heterogeneity in porous media, or a temporal character, as recharge events to an aquifer. Provided that an adequate representation can be found, then these aspects of flow and transport frequently are better modeled by taking the complex or unpredictable element to be a stochastic process. Given an adequate representation, then the following questions may be addressed: (1) What is the implication of these elements for flow and transport in porous media? (2) Given observations of the physical process (hydraulic heads, concentrations, discharges), can the stochastic element be characterized (variances, length scales)? (3) Can an adequate monitoring program be designed when the physical process incorporates complex or unpredictable elements? The principal objective of this research is a better understanding of flow and transport phenomena when the underlying physical process contains one or more stochastic elements. A subsidiary objective is the development of a network model to evaluate sampling schemes when the physical process contains a stochastic element. An inverse procedure whereby the statistical properties of the stochastic element can be determined from the outputs of the physical process will be a necessity if these models are to be utilized. Where practicable, investigation will include development of usable computer codes.

A large amount of geophysical data is recorded in water wells and test holes but interpretation is subject to significant uncertainties. The data are used in ground-water models; to evaluate potential waste disposal sites; the effects of ground- water contamination, and to guide aquifer development, including geothermal reservoirs. The development of quantitative log interpretation techniques to derive more accurate data and to evaluate the statistical uncertainties in the data will reduce costs in ground-water investigations. Project objectives are to evaluate presently available logging equipment and log interpretation techniques and develop improved instrumentation and analytical techniques for specific ground-water problems such as: site selection and monitoring for disposal of radioactive, municipal, and industrial wastes; improve log derived data such as porosity; attempt to relate the log character of fractures to their hydraulic conductivity and to refine computer techniques for plotting hydraulic conductivity profiles from logs; develop the capability of making quantitative interpretation of borehole gamma spectra; and to make a statistical analysis of the magnitude and sources of errors in log derived data.

There is a general lack of knowledge of fundamental processes governing the fate and transport of anthropogenic organic compounds in surface and ground waters. Interactions of organic contaminants with natural organic coatings on sediments and aquifer porous media are not well understood. Furthermore, abiotic and biological transformations of organic contaminants in surface and ground waters require extensive fundamental investigations if their effects on Water Quality are to be understood. Objectives are to (1) determine physicochemical and biological processes, controlling the fate and transport of organic compounds in surface and ground waters; (2) determine bioavailability of hydrophobic organic contaminants to stream biota; and (3) study transport of organic compounds from rivers through estuarine systems.

The physical/chemical variability in our rivers and estuaries is large, but causes and interactions are not clearly defined. Variations forced by weather and climate appear to be very important, but we don't yet understand how riverine-estuarine systems operate on very short and moderately long time scales. Furthermore, the effect of anthropogenic activities also may be important. Without such information we cannot understand and predict how these systems respond to variations in climate and human activities including changes in the amount, character, and timing of freshwater, toxic- waste, sediment and plant-nutrient inflows to these environments. Project objectives were to better understand the variability of the physics (circulation) and chemistry (primarily oxygen, carbon, silicon, nitrogen and phosphorous dynamics) in riverine and estuarine environments, and to discriminate between natural variations due to atmospheric/oceanic forcing and human-caused impacts.

Organic substances in streams affect the water quality and uses of the water. To determine the effect of organic substances on water quality, the physical, chemical, and biological processes involved in the transport and degradation of these substances must be understood. Procedures for measuring or estimating the rate coefficients describing these processes must be developed. Models using these coefficients must then be developed for predicting the fate of organic substances in streams and their effect on water quality. Project objectives are: (1) to study the fundamentals of volatilization, dispersion, and sorption on sediments of organic substances in water; (2) to develop sub-models of these processes including methods for measuring or estimating the process rate coefficients; and (3) to integrate these sub-models into overall transport and fate models for organic substances in streams.

Heterogeneous geologic material affects ground-water flow and transport on all scales. On the local scale, changes in hydraulic and geochemical properties can occur over distances on the order of centimeters. On the intermediate scale, the heterogeneity of intra-aquifer depositional layers in unconsolidated material and fractures in consolidated material influences the pathways of ground-water movement. On a regional scale, the heterogeneities due to a really extensive aquifers and confining units affect the flow system in a system wide manner that influences both the boundaries of the system and the generalized pathways of fluid movement in the system. An assessment of the importance of heterogeneity at all scales is required to better understand and define flow and transport in ground-water systems. In addition, the relationship of field measurements obtained in heterogeneous materials to the actual occurrence and movement of the water and chemical constituents in the system must be defined. The objective of this project is to quantify the effect of specific heterogeneous geologic controls on ground-water systems. Meeting the objective will entail the development of methods for incorporating the effects of heterogeneous hydrogeologic controls into simulations of ground-water systems. Ideally, the characterization and quantification of the heterogeneous earth material will incorporate basic geologic information on the deposition and history of the materials under study, as well as hydraulic and chemical information.

Research goals are (1) to develop reaction-transport models with varying levels of complexity and data requirements, providing guidelines for the appropriate application of these models given field conditions and limited resources; (2) to incorporate the effects of surface-chemistry phenomena into reaction-transport modeling; (3) to develop methods to identify and quantify important chemical and biological reactions affecting transport of inorganic and organic substances; and (4) to compile estimates of reaction rates and reaction-rate laws for chemical and biological reactions.
In addition to model development, the project undertakes field, laboratory, and theoretical studies to investigate field-scale chemical transport in groundwater and watersheds, soil CO2 flux in arid environments, isotope fractionation processes, the thermodynamics of surface complexation and other chemical reactions, and the climate record in Devil's Hole carbonate deposits.

Managing water use in riverine and estuarine systems requires an understanding of the governing supply, circulation, mixing, and flushing processes. Qualitative and quantitative evaluation of the hydrodynamic and transport properties of such water bodies can be computed via mathematical/numerical simulation models. To accurately simulate both the temporal and spatial variations of the flow, which significantly define the transport processes, the simulation model must be capable of accounting for hydraulic and tide-induced fluctuations, water withdrawals, discharges, winds, nonuniform geometric configurations, and other manmade or natural factors. Objectives of this project are to investigate and develop various mathematical/numerical techniques with which to simulate the hydrodynamics of one-, two-, and three space dimensional transient flows in various waterbodies; evaluate and/or develop methods to describe the transport of solutes in such waterbodies utilizing the comprehensive flow information derived from flow simulation models; and develop and implement an operational system in support of flow/transport simulation models.

Stream systems function as integrated units from the zero-order basins at their heads to their terminations at the sea. Interior adjustments to changes in their headwaters or along their lengths occur in a variety of ways, some of which leave sedimentary deposits that provide important information with regard to the sensitivity of the systems to disturbances of various magnitudes and with respect to the nature of past disturbances. The former type of information is crucial to reliable interpretation of paleoflood deposits and the latter knowledge is essential for testing hydrologic predictions derived from climate models. In order to interpret fluvial deposits properly, however, an extremely accurate knowledge of stream system mechanics is required. The long-term goal of this project is to develop precise, process-based algorithms for flow, sediment transport, stream channel adjustment, erosion, and deposition in characteristic segments of a wide variety of fluvial systems. These algorithms then can be used to assess local environmental problems along particular types of stream segments, or they can be coupled with each other and with analogous algorithms for hill slope processes in order to produce models for erosion, sediment transport, and deposition on a regional scale and, thereby, provide a sound, process-based connection between regional hydrology and the salient characteristics of the sedimentary deposits in a wide variety of stream systems.

Analysis of heat and fluid flow in geothermal systems is needed to adequately describe both the natural state of such systems and their response to fluid production for energy development. The analysis may involve analytical or numerical solution techniques, but requires delineation of realistic conceptual models for specific geothermal systems. This, in turn, requires the collection and synthesis of geologic, geophysical, geochemical, and hydrologic data. Periodic monitoring of changes in geothermal systems, including surficial thermal manifestations, can aid in understanding the natural conditions of flow and effects caused by crustal unrest and geothermal development. Objectives are to elucidate the processes involved in geothermal systems and their response to stresses imposed by geothermal development, earthquakes, and magmatic intrusions Develop realistic conceptual models of specific systems; evaluate the level of natural variability in thermal fluid discharge in hot springs and fumaroles at specific geothermal areas.

This project is focused on developing objective methods for evaluating USGS hydrologic-data-collection activities; such methods are needed so that activities can be modified when necessary and the efficiency of USGS operations maximized.

The increasing need for understanding the effects of human activity on the chemistry of natural systems requires a continually increasing degree of sophistication in the models used to describe the processes through which these effects occur. Such models include thermodynamic and (or) kinetic models of: aqueous speciation, the chemistry of dissolved gases, gaseous and aqueous diffusion, transport of constituents across interfaces, redox processes, mineral-water interactions, the chemistry of anthropogenic inputs to natural systems, and isotope effects associated with these processes. Project objectives are to (1) identify the factors influencing the reactions and transport of solutes in natural waters; (2) evaluate reactions and transport processes for volatile constituents in unsaturated zones; (3) identify processes occurring at the saturated-unsaturated interface (the capillary fringe); and (4) investigate the application of isotope effects as a tool for understanding these processes.

Biogeochemical processes associated with the microbial community (algae, bacteria, fungi) constitute the interface between solute transport and biotic production in riverine environments. Identifying and estimating the role of biotic processes such as nitrification and denitrification by bacteria, nutrient uptake and production by epilithic algal films and decomposition of particulate and dissolved organic matter, as well as abiotic processes such as absorption, are important for understanding the linkage between terrestrial, riparian, hyporheic and in-channel contributions to the nutrient chemistry of a drainage network. Relative biotic response to solutes in transport between pristine and anthropogenically modified riverine environments is poorly understood, but necessary for long-term management of surface waters. Project objectives are to identify and determine rates of biotic transformations of transported solutes at chemical-biotic interfaces in fluvial environments, including seepage areas, riparian zones, sediment/surface-water interfaces, intragravel- subsurface flow interfaces (hyporheic zone) and floodplains.

The biological and chemical characteristics of aquatic environments depend on a generally complicated balance of physical, chemical, and biological processes. Basic to describing these characteristics is an understanding of transport processes including both advection and mixing. For a given water body, these processes depend heavily on the mass, momentum, and energy transfers at boundaries and the internal response of the system. Many of these transfers and responses are poorly understood. Broad goals of this project are to quantitatively understand the physical processes responsible for the transport of conservative and nonconservative solutes of biological and chemical importance. Through the use of time series analysis and other methods, conceptual, statistical, and numerical models of these processes are being developed.

Understanding the effects of climatic variability is important to development of water resources, mitigation of flood hazards, and interpretation of geomorphic surfaces. Climatic variability, which is characterized by temporal changes in variability of seasonal climate that spans decades or centuries, may be more important to water-resources evaluations than changes in mean climatic conditions. Changes in variability of climate has a large effect on the probability of occurrence of extreme events, such as floods or droughts. Understanding of climatic variability and its effect on the landscape is of paramount importance for estimation of flood frequency, sediment transport rates, and long-term watershed and channel changes. The objectives of this project are to define historic climatic variability in the western United States over the past century, to identify specific time periods of statistically stationary precipitation, discharge, flood frequency, and sediment transport, to assess the net effects of climatic variability on watershed conditions and fluvial systems, and to determine the extent that historic changes reflect Holocene climatic fluctuations. See Changes in Riparian Vegetation in Arizona for examples of how repeat photography has provided an invaluable record of changes in the riverine environment. Also see Mojave Ghost Town for repeat photography documentation of vegetation recovery in Mojave Desert areas that were settled in the late 19th and early 20th century and later abandoned.

Many hydrological and geochemical processes associated with lakes and wetlands are poorly understood. Characteristics of wind and vapor profiles over lakes, which are basic controls on evaporation, have been studied in detail for only a few large reservoirs in the western United States. Many commonly used methods of estimating surface runoff to lakes and wetlands, are inaccurate. Hydrogeologic controls on seepage to and from all surface-water bodies have not been studied adequately, either from theoretical or field perspectives. Research on these components of lake and wetland hydrology is especially critical to individuals responsible for management, protection, and restoration of these resources. The major objective of the problem of lake hydrology research is to gain understanding of the basic principles controlling the interaction of lakes and ground water, including associated chemical fluxes. The project emphasizes integration of theoretical and experiment field work. Although research emphasis is on ground water, the project includes state-of-the-art studies of the atmospheric and surface-water components of lake hydrology, as needed in the evaluation of the ground-water component. Evaluation of error in hydrologic methodology for the various aspects of lake water balances is an integral part of the research effort.